Do not underestimate combo decks, especially ones as fast as Dragon. Verse Dragon a large part of any Oath deck turns to a steaming pile pre-sideboard. This is especially true with Falc's build, because he doesn't main deck Morphling (Hard casting Akroma is tricky enough, getting it back after its been countered is another matter). Dragon can squeeze out a kill as early as turn 1 on a shoelace of mana and resources, and is commonly supported by more free counters than the average Oath Deck. On the upside Gaeas Blessing will stop Laquatus but it won't stop either Cursed scroll or Stroke of genius from the sideboard, most good Dragon players will have at least 1 alternative kill available from game 1. Even so Dragon isn't the hardest of matches (its just a long awkward one), especially if you splash black for Duress or run an Ophidian conversion in the sideboard.
Falc,
Quote 1) Is the deck too dependent on Scepter and if so, should it then run four copies?
Oath is already massively dependant on Oath of Druids, the best Oath builds will minimise this by providing insurance plans i.e. a solid counter base, spot removal and non-targeting effects. By making an Oath deck that is not only highly dependent on oath but also on Scepter is kind of compounding the problem that Oath suffers. So I certainly wouldn't run 4, and I wouldn't gear the deck too much around this card, by that I mean don't run cards which are solely included because of there synergy with Scepter. In saying this I don't won't to suggest that I am against the inclusion of Scepter in Oath, In fact I think that Scepter can elevate the redundancy of Oath of Druids in certain matches. I have yet to test the card in my Oath build but my gut instincts are telling me to initially trial 2.
Quote ) Is the Wish-board the way to go with this or should I just drop/reduce the Wishes and run a more normal Sideboard?
I think your sideboard needs help certainly but IMO wish is a house in Oath. Oath is a tight deck anyway and Wish provides access to some serious answers without compromising other deck slots. But you need to be seriously strict on the tool selection because on sideboard slots are usually in high demand to. I would keep wish in the main deck, and sideboard stifle. Stifle is less flexible than countermagic and if you need stifle and cards alike you can fetch them.
Quote 3) Can the deck survive without a board-clearing spell (Keg, Deed, etc), or is one absolutely necessary?
Both Deed and Keg offer versatility, out of the 2 I prefer Keg because it doesn't hurt Oath. To be honest I have only ever once needed to tutor for the single Keg I main board in my current build, So the frequency that you require controlled selective board sweeping effects is not often, because most of the time Oathing up weaver solves 99% of the problems keg does and the remaining 1% of the problems and the occasions when oath doesn't turn up can be cured by Balance. But in saying that I probably would of lost that game where I didn't tutor for Keg if it hadn't of been there.
Getting to your deck Falc;
Mana Drain, where are they? Expensive I know but the performance difference you will notice is massive. Oath is a really colourless mana hungry deck. The Weaver/Feeder lock loves Drain, plus is helps with tricky matches by giving you the option to drain in a Morphling from your hand. You are running Scepter which will mean your build will benefit form them even more, then the standard build. Save up! run 4 instead of counterspell.
Misdirection is also missing from your build. Think about what it doesn't "counter" Force of will is good, so what does that do that Misdirection don't? Counter creatures, who cares? Plus Misdirection doesn't cost you 1 life.
Basic lands are a must, Back to Basics and Blood Moon are really bombs against you. Ok you have counters but a single Forest and Island can get you that Vital disenchant when your counters fail you, and they eventually will. Yavimaya Coast sucks so that's what should come out IMO.
How are 3 wastelands working out? Good? well 4 will be even better, If you can make the room and I now it is hard but they will help with some of the hardest matches you will have to face.
No Sylvan Library? Is Scepter worth it? Probably. You need to cut something for at least one, Sylvan is one of your best weapons against control and aggro-control, plus it stops you drawing your creatures and excess land. Really try to find room.
I personally wouldn't main deck Akroma. In most circumstances Akroma is better than superman, but Superman is good in 100% of situations. This is obviously a Meta-game call, but a carefully timed StoP will see beaten.
Abeyance is the obvious card for Scepter, stand only it is a decent card especially against control elements allowing you to push through Oath, or a hardcast Kill.
Sideboard time, I think this is the weakest part of your deck.
Hydroblast, Why? Naturalise will destroy Blood moon, Misdirection is infinitely better against every other Sligh can throw at you.
Funeral pyre and Argivian Find and both nice tech, but I think not game-breaking tech. I have seen both used before, and admittedly never tried using either but I have never needed to.
Orims chant? Yeah that goes nice with Scepter, but isn't this an Oath deck? What's the point? creatures don't concern you. Abeyance is much better because it stops what you need to stop and cantrips, so it better alone and with Scepter.
Naturalise and Crumble, Hmmm Chalice of the void is almost certainly going to be set at 2, so it will hose Oath, Scepter and Naturalise. Running a card like dismantling Blow will automatically get around this and save you a deck slot and give you 2 cards.
I don't think Fire and Ice fits the deck, its only very strong when you have Scepter, alone is not very good but it does give you an alternative kill. Your call.
I would only sideboard Nishoba if you face a lot of Sligh, if you face your average amount Sligh opponents and are confident with the match up then run Akroma only. Even so circle of Protection: Red is better verse Sligh anyway.
Do you really need 3 Swords to plowshare for cunning wish? I Have 1 main decked and 1 Sideboarded and this has always proven enough, really you only need it when you get odd creatures that can evade the oath trigger, stop your kill or kill you without attacking. There aren't many, other than that it serves to stop an 1st Negator.
Visara Sucks. It's slow at killing welders, and Akroma is often better verses Tog.