Recent Windows versions requires that all drivers be cryptographically signed. Assuming that you don't disable signature checking, and that you check that the driver is signed by the original company, you can be assured that the driver itself is probably unmodified from what is in the original company's website.
However, there's no guarantee that you're running the original installer. It's possible that a rogue driver site wraps the driver with rogue installer, that then installs some other malware in addition to the unmodified driver.
In short, it's probably unwise to install any software (including drivers) that is downloaded from untrusted third party sites.