Your C-12 time does count toward the 50 ME requirement, as that doesn't have to be PIC. That saves you some significant money, because you will only need to fly single engine airplanes to get your 250 PIC. You will need to fly those until you reach 250 PIC. No way around it for the ATP. The airlines can't do much with your time until you have the ATP. Once you get that, they are much more accepting of the powered lift time.
I've heard of a few regional airline training departments getting individual exemptions for V-22 guys with the local FSDO, but that is on a case by case basis and I have also heard about the FAA in Oklahoma City smacking that down.
I'm still a little over a year out, so can't give you much more insight. Try to find a buddy you can share safety pilot time with to get to 250, get your ATP, and then you should be golden, at least with the regionals.