There aren't known backdoors in FileVault2, or for that mater, Microsoft's Bitlocker. Apple, on the other hand, has been pretty forthcoming with law enforcement backdoors in iPhones (which, actually, seem fairly reasonable, IMO)

Don't trust their encrypted filesystem? You better not trust the OS either, for that surely has access to all of the encryption keys you've ever put in main memory.

tl;dr: if you don't trust proprietary encrypted filesystems, you better not trust the proprietary OSes they're built into either.