The only caveat is that if RdRand was made to output the bits about to be sent out XORed with a stream of AES(n++, NSA_KEY) then you get seemingly random data t

The only caveat is that if RdRand was made to output the bits about to be sent out XORed with a stream of AES(n++, NSA_KEY) then you get seemingly random data that is 100% deterministic once you know the key and completely invisible if you don't know the key.