Or you could just use the tool made for the job. Wiki engine for the wiki, forum engine for the forum. It's not like mediawiki is some fringe-odd-one-out-wiki-markup, it's used on freakin' wikipedia (which should account for a lot in itself) and many many thousands of other wikis.
And yes, a lot of the activity on the DT wiki is from Daniel. There probably needs to be someone putting in a lot of hard work keeping a wiki organized. Perhaps there is someone who would do that in a subforum here, or that person is simply missing on GH and that's why the wiki is in the state it is.
No, the cover-all-keyboard-stuff wiki on GH does of course not need to be a copy of the cover-all-keyboard-stuff wiki on DT. But I, for one, would pick one wiki and concentrate on adding material there. I don't believe users in general are going to care too much to add the same things in two locations.
There are going to be two camp for sure, nothing wrong with that, but I just can't see the markup language being a major obstacle. Mediawiki is quite simple, there are a few common things you'll learn quickly, and then you google the more uncommon commands when you need them. I don't know bbcode almost at all, but that doesn't stop me from posting on the forums...