Amusingly enough I find myself just trying to dive into those gates while doing tri-geons. Funny thing about them - they work like Transition floors in that if you find an angel gate you go to an angel floor. Nice way to avoid losing rarity level (if you manage to sneak through that is lol). I only managed to successfully snag the big trove that appears on that floor 3 times (out of 10 trips in).
Only one time did I not want to go in, and that was when I was building up rarity level. It cut me off right in front of an angel gate on a Normal floor.
It's just a pain when you get put in right next to an immortal in a short, tight alley.
@ChiTz: It's the Invisible guy in the Hiyo ship near the right side by the Job Change Hiyo (he's hard to see, look for a strange flickering on the ship).