Anything can be abused.
Fractional reserve doesn't seem possible with BTC, no way you could lend btc you didn't have. But it would be possible to create a system that lent $ (or some other fiat) based on holdings of BTC. I don't see why anyone would, but thats a different question.
Fractional reserve banking doesn't allow lending money that doesn't exist, it just permits lending money that you don't personally have even though someone else does.