Alright, so I tested it properly with a mate and we can only conclude;
Zair > footstool = legit.
I'm still a bit surprised, even though it was clearly working back when I tested it by myself, and even though I was expecting it to be at the very least very close. But there you go.
With the heavier characters like Wolf, as you alluded to, they land before they get out of hitstun so it's a fairly easy grounded footstool. With lighter characters like MK, it's still possible but you actually footstool them before they hit the ground (and before they can get anything out), which would set things up very nicely for a lock, if only we could do such things (because Toon's too floaty, his first footstool goes too high, so if you try to fastfall quickdraw, it'll be too late. What you can do however, is Zair to footstool with a bomb, wait a bit, bomb throw down, second footstool, fast fall quickdraw and that will lock, but who's gonna do that?). Now where was I? And with the really dumb characters that get out of everything easily, like Samus, we were pretty sure that it's still possible, just a lot harder.
Everything else has already been said like, yes, you have to completely give up your spacing with Zair. Yes, it works easier on lower percents. So on.