Nope you can't fly at GM Island. I can't speak about what the island was like before I actually played WoW. But since the first time I ever reached the island, up until a couple of days ago when I most recently returned, I was unable to even mount there, little known fly.
I don't know for sure, but I think they may have put one of those invisible nets around GM Island that the outer area of Deepholm is now encased in. Where if you try to mount it will cast and you'll be mounted for a millisecond, and then get auto dismounted. So maybe a Druid could fly there, like in Deepholm. I made the trip on a different class this time though so I'd have to shoot out there on my Druid to be sure, which I'll probably do eventually.
As for the method. Well obviously anything that's getting you to GM Island has the ability to either fly, walk on air, or some other form of bugging elevation. However I just climbed the mountain the old-fashioned way. I could have flown there, and in fact have the ability to fly in any instance using various means. But that would defeat the purpose of the entire thread so I don't heh.
I'll send you a PM.