Yeah, not USB but in principle it's the same whether it's PCI or whatever. There's no way to prove an RNG is truly random really just have to rely on validating subsets of its output look random. NIST has published recommendations for sampling RNGs.
Here's the title:
A Statistical Test Suite for Random and Pseudorandom Number Generators for Cryptographic Applications
I don't think there's a real need unless it's regulated to need some dedicated HW RNG.
Yeah as long as the setup for the device symlinked its device path to
/dev/random
or you did that yourself. Stuff I used had a Java SDK