There is no problem on doing that. I do that often. But then again, I'm "The Sucky Bass Player"

. No I don't think there is a problem in that. Just make sure to mute the strings above the highest string.. Like if you are playing the G string (no pun) and have your thumb on the D, make sure to mute the A and E string with your palm.
This thread should also be in the Technique forum
D