I could say my opinion on the for these two as well:
Gen IV & V Pokemon:
If they're implemented correctly (right movesets, base stats, TM learning datas and all that), I don't see why not to add them in the hack. If you're going to go with Jambo's patch there, sure have more added in.
Depends on the situation really. If there is no need for adding fakemon in the hack, it's not like adding them would make a difference to the gameplay unless they're implemented really well (and so it would be fun to have some in). So in this case, I just don't see a point in starting to add them because that would be just pushing the spriters to do a lot of work for no reason really.
But in some hacks (for instance Ruby Destiny series), there are "fakemon" because of a reason behind having them. If the storyline is built so that non-pokemon creatures should exist, the hack would require these "fakemon" to be there. In this case, I wouldn't consider these new creatures even being fakemon, as they are no way "fake" (or maybe properly "made") at all.
So what I would vote for is that don't bother adding fakemon if there is no purpose for adding them. Otherwise, it would just feel weird to have them around (unless all the pokemon were fakemon).