As for me, if we're not taking in the reformation factor for CPA, I think that the others would be mildly surprised and disgusted with Indigo and Rainbow, but then accept them for how similar they both are. Same could be said for CHS, but not on as bad a level as the Crystal Prep students.

I would say they would be surprised by the relationship if Rainbow doesn't receive some teasing from Rarity and AJ. Indigeo might be a different story especially if Cinch found out about it.