Actually, I just recently created an all-flying team on Emerald, specifically for a monotype challenge however. This was my team:
-Swellow
-Crobat
-Gyarados
-Altaria
-Xatu
-Gligar
I also realized that flying is probably the most versatile type you can use. With DP, you can get any type using all-flying except for fighting, and even without it, the only other type you'd be lacking is ghost. In other words, if you have any good coverage for the three weaknesses of flying on your all-flying team, you'd hardly be doing a monotype challenge at all. That's why I also did a poison monotype run on the same game. This was my team for that:
-Crobat (again)
-Vileplume
-Swalot
-Weezing
-Seviper
-Tentacruel
This one was actually much more difficult, and currently is much more incompleted than the flying one, not only for the reason that I have to be able to defeat a team that has about 25-30 levels on me and contains all the types that poison hates the most, but I also have to go through the entire Battle Frontier using the same type, that would be if I didn't drop it, which I think I will, because I've lost interest in that one. I think next time I'll do the bug type. As for the specifics, I'm not yet sure. (Okay, I'm pretty sure I've answered the main question by now)