I'm using BTSync with EncFS, but if you don't trust the BTSync binary – it's probably got access to the non-encrypted data as well unless you've jumped through a few more hoops than a "typical BTSync installation". I'd guess 99.9% of BTSync users have the binary installed with at least enough permissions to read anything the logged in user can read (which includes the cleartext-mounted stuff in your EncFS or TrueCrypt volumes).