To be honest, for it to really be SMA, their should only be a single major religion in existence, and it should be a renamed version of Christianity. A bit of Judaism and Islam can exist as minor religions (with the Islam copy being a major religion on another island), and scattered tiny pagan religions. Anything else is a deviation from an actual medieval atmosphere. . . .
. . . but since we don't have that, nor do we really want that, I don't think it's specific details of religions that are important, nor the philosophy behind them, but if they are serious attempts at religion or spirituality (for a rather lose definition of religion), not completely out of place or immersion-breaking (again, lose definition here), and organic and alive.
I doubt anyone would deny they SA adds quite a bit to Dwilight (you may hate it, but you cannot deny it gives a great feel) and seems right. But it is very arguably NOT strictly SMA. It is not exactly an Eastern Philosophy religion, but it certainly has a lot in common with them . . . it believes in divine powers (the Bloodstars), but I would say it doesn't really worship them, at least not in a western sense. It's a mix of western philosophy, eastern philosophy, and a little belief in divinity, but even though I doubt you'd ever be able to find anything like it in medieval Europe, it's Dwilight's most successful religion, and adds greatly to the atmosphere.