Yes, RDRAND could do evil things. It could go play Towers of Hanoi when you execute it. It could Halt and Catch Fire. It could email your MAC address to the KGB. So could any other instruction, if Intel wanted to be malicious, just when you thought it was safe to go back in the register pool.
If the NSA has convinced Intel to do evil things with RDRAND, the most likely one would be to hand out low-quality entropy when claiming that it's high-quality. It's still useful, and like any entropy source, it shouldn't be the only entropy source you use, and you shouldn't use it without hashing it together with a bunch of other hopefully-not-broken entropy. But it's still useful, and as somebody said, the NSA isn't your only enemy.
Especially when you're starting up a machine (physical or virtual), you really need good entropy and you don't have a lot of sources available yet. If you don't trust RDRAND, or even if you do, hash it together with some secret password and the clock and whatever else you've got.