...but, it's safe to assume that at the moment Snog has about as much control over these creatures as the world's original creator, Candy, does.
Basically, they are not Christian angels. They are, most likely, where the Christian legends took the idea from, in the same way that some consider dragon legends to have emerged from Komodo dragons - close, but no bisquit. These angels do not serve the God; they don't serve even a god, as the Crüxworld has none (no real ones, at least - idols are a whole another kettle of fish); for that matter, they don't serve anyone. Perhaps not even themselves as much as their memory. They're not ultimately good, they don't represent ideals, they don't fly around playing harps and singing to sheep herders... they don't fulfill what we think of as the "traditional" angel myth. They don't even fit what the Bible says about angels. (I think. I need my references.)
The angels of the Crüxworld were once huma beings, alive and breathing. They became angels after they died. Not quite material, not quite immaterial. Something in between: ethereal, perhaps. St. Croix may be an angel, but I'm fairly sure he is not the stereotype of one at all.