I was the only Hayabusa main at GVN. I saw two other people using him, one that I didn't know and...was hopefully just messing around with him and Gren Kuts. Not sure if Gren Kuts mains him or was using him just for the hell of it.
In any case, to expound a bit on the lows hitting aerial moves and low crushes sometimes, it's not too much different than a character trying a jump kick to crush a rising kick and missing it. The window is relatively small but low-crushing attacks are still vulnerable to lows. If I had to guess, all that happened is the active frames on the attack are a bit later than we're used to from previous DoA titles. I'll grab Rikuto to try and explain a bit more but that's what I figured from it all. A lot of attacks getting stuffed that didn't look like they should at that point. Again, Eliot seems to be capable of shutting down nearly everything at range if he wants to and I wouldn't be surprised if the whole reason was the frame data on a lot of the moves I was using is simply a little different.
I believe that because Master won the first IPL event at e3, he's not allowed to attend the others. No idea why he wasn't at GVN though.
Can Hayabusa still Izuna off of some ledges like he could in 2U and 4?
Manny has only been barred from competing at one event so far in the States. He absolutely could have come to GVN. I'm not sure he would have come anyway, but I do know he was helping out Tecmo at the Gamestop event in Texas literally the day after GVN ended. That very well could have been the whole reason.
As for the Izuna, yes he can, and he can also Izuna through floors like on the Oil Rig.
EDIT: Actually, while I THINK I remember doing it, I don't know that I ever actually tested doing the Izuna off a cliff. I'm asking a couple people to confirm right now and I'll remove this edit if it does still work or confirm that it doesn't. I'm almost positive. No clue why I didn't make it a point to check because I know I wanted to test it before I got my hands on it...