Drivers are a fundamentally unsafe concept, like an ffi call, you're talking to hardware the compiler doesn't understand and assuming it's going to do what you want. So there will of course be some unsafe. In a well implemented driver it will also be very limited in scope and relatively easy to check.
I can't vouch for the code quality (I just don't know how good it is, I had no hand in writing it, and it's not used in a production system), but I believe you can find a usb driver implementation written in rust here: https://gitlab.redox-os.org/redox-os/drivers/-/tree/master/x...