I'm guessing, but the speaker's point may be that Mel's religious views may be incompatible with the spiritual core of the AA program but are so strongly held that he wouldn't be able to let go and go with the program. I'd have to know a lot more about Mel and his core beliefs to evaluate whether the comment is correct or not. Just with what little I know the fact Mel has a strong belief in a higher power already should be a plus to him accepting the AA program. Dunno.
Maybe, maybe not. The spiritual awakening needed to live the 12 Steps isn't allied with any religious beliefs. Nor is it antagonstic to any.
Much is based on the book of James and many of St. Paul's teachings, but you probably wouldn't know it.
Yes, I imagine that a passionate (pun intended) and often publicly expressed belief that the vast majority of AA participants are going to hell because they aren't faithful members of the Roman Catholic Church (never mind that Mel is a member of breakaway sect operating in direct defiance of ecclesiastical authorities) could be a bit of an obstacle to effective participation in an AA program.
Mel's a traditional Catholic. He won't have any problems with the spirituality of the AA program. It will probably be easier for him than for a person who, up until he needed one, hasn't had a higher power to believe in.