I can't answer that, I don't have any health issues, but I ate them in moderation (and always cut the green ribs off, which is where the most oxalates are).
I think my favorite use for the carambolas (so far) is juicing. I processed a lot of the fruit with my Vitamix, some ice, a piece of fresh ginger, and some lemon/lemon crystals (True Lemon). Drain the liquid through a sieve to remove pulp/fiber.
It takes a lot of fruit to make a decent amount of juice, but it helps solve the "what am I going to do with all this carambola?" conundrum.