Not a solution to the particular issue of trusting HW PRNG unless you can audit the innards of this particular hardware.

Maybe an opensource FPGA-based solution might do the trick if you really need high-quality highly-secure fast random number generation.

Personally when I've needed good and fast sources of entropy I've just picked a good (but slow) random number source and used it as a key for a strong stream cipher (that I would renew every megabit or so). Assuming there are no weaknesses in the cipher and you have hardware acceleration you can get a very fast PRNG source.

And unlike RDRAND you can actually audit the hardware cipher implementation because it behaves deterministically.

Some of the older devices (1997) had obvious flaws, and were lousy for crypto.

Here's a list:

https://news.ycombinator.com/item?id=6060636