[Will]

Actually, dogscoff does have a good point about a tightly integrated theocracy. Not sure how much that would be the case, since there technically are two religions. If there would be a huge reaction against Atheists for denying God, it would be reasonable to think that there would be a reaction against the Buddhist-inspired religion, for essentially having a very different concept of what exactly God is. For there to be minimal clashes, there would have to be several individuals that follow the Buddhist sect in high positions of power, and the state operation of the "main" religion should impose minimally on the "other" religion, which would mean that a lot of the core beliefs must reconcile. That doesn't seem too difficult, as there would likely be a lot of overlap, and you haven't provided any details as yet that distinguish religious activities from what could be normal secular activities (i.e. the intense physical training for all).

As for the reaction to dark-skinned humans... I doubt the first reaction would be a blood/genetic test. But I also doubt that the first reaction would be "kill it!" Like I said, they would not be accepted as equals. If you're imagining Icarans being somewhat benevolent, I could see that. If there would be interaction, I would put it somewhere along the spectrum from being treated like sentient pets (with almost zero education) to a class of servants and/or slaves. The position on the spectrum could very well differ depending on location, even on the same world. And the sustain process would almost certainly be forbidden for any except "pure" Icarans.