I have no idea if RdRand is the only source of entropy for /dev/urandom in the kernel these days but that does seem quite silly
If I understand correctly, the idea is to use RdRand to feed the entropy pool (which is also fed by other noise)[1] from which urandom pulls. So it doesn't seem RdRand would be the sole source of entropy if it were to be used in this context.
Most servers do not have any serious source of randomness (unless you buy another hardware RNG) which is partly why these were introduced (Intel used to have a motherboard RNG, and VIA had on CPU ones years back).
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If I understand correctly, the idea is to use RdRand to feed the entropy pool (which is also fed by other noise)[1] from which urandom pulls. So it doesn't seem RdRand would be the sole source of entropy if it were to be used in this context.
[1]http://linux.die.net/man/4/urandom
Most servers do not have any serious source of randomness (unless you buy another hardware RNG) which is partly why these were introduced (Intel used to have a motherboard RNG, and VIA had on CPU ones years back).
You can buy one of these http://www.entropykey.co.uk/ which are unlikely to be NSA "certified" instead.