There's a set of "CC immune" ultimates.
Doesn't mean they won't get CC'd, but they'll complete the ultimate anyway, then be cc'd at the end of it (if there is time remaining, EG: Taric stuns Malp mid dash for 1.6 seconds, dash takes 0.4 second, Malp will land, then be stunned for 1.2 second.)
Same with others, Azir wall is a knockback (initial cast and on trying to go over it.) So none of them will be stopped from going over the wall, but once their ulti's are complete, they should get bumped back if they're still inside/touch the wall again.
Edit: On a side note, feel like those should get the Yi treatment where his says "CANNOT BE SLOWED" in combat text, malp, hec, and vi should get "CANNOT BE STOPPED" or something, so it's less confusing overall for people who aren't bookwormy..