I am not too sure but I don't think so. In the case of something like BitPay assuming it works as I described above they probably would also allow you to transfer back into Bitcoin. Instead of you sending Bitcoin to BitPay they will subtract the credited amount from your account and send Bitcoin to any wallet address you specify. Again the Bitcoin you're getting is just Bitcoin from BitPay's reserves. It isn't the same Bitcoin you deposited. There are some interesting implications in the details of that people can take advantage.