Well first of all, I'm really glad to hear there's a raptor on bloodmyst at all. I love those guys and I hated having to trek through lv 40 areas to get one when I was a noob.
As far as immobilizing during taming, if anyone interferes at all, you will almost definitely fail the taming. If someone even heals you, and I think even buffs you while channeling, you fail.
I learned a nifty little trick to freeze an enemy in its tracks during taming. Unfortunately you will need the freezing trap skill learned at level 20. I posted a quick guide to my technique for taming without taking damage in the Hunter Forums. If you use this process, I think you will be able to tame this guy before he thaws and can knock you down.
As far as retaining his ability, I'd say just tame him and find out yourself. I think it's probably not going to keep the ability though. Most pets lose their elite stats and any unusual aspects when tamed. But unless they changed it, they sometimes are a little better than other pets. For example, King Bangalash has the same DPS as a normal cat, but hits something like every 1.4 sec instead of the normal 1.5 sec.
I checked on the raptors as pets and couldn't see any abilities other than the normal bite, claw, and dash. Still it's worth a try. Let us know what you learn.