Honestly, I'm not convinced that there's any categorical difference between the gay->straight and dominant->submissive continua. Both attempt to categorize people based upon their sexual desires and arousal, and both are continua with extreme points at the end and shades of gray in between, rather than discrete yes/no values.
More accurately, someone who doesn't have sexual feelings.
Not all Christians are straight and/or cis, certainly, though I would say that Christians are at least somewhat more likely to be straight/cis than nonreligious people. This isn't because of anything inherent in Christians, but simply because Christians who are non-straight and/or non-cis are probably more likely to question, and ultimately move away from, their religion than straight, cis Christians (being condemned by many in your own religion, or knowing that you would be condemned if you came out to them, tends to prompt religious questioning and soul-searching).
QUILTBAG really is an acronym, though.