sorta..
if its a Class D (digital circuitry) amp then its fine. however most amps, especially older ones, are not Class D and u will destory the internals from the bass vibration.
i think its really not a big deal.....how many people these days are running class A/B amps, especially for subs?
and also there is a hell of a lot of vibration in cars as it is, as long as your sub box is nice and solid i dont see it being a big problem