In real world use, as long as you have rubber feet or something similar, it'll probably work just fine. Technically speaking, if there is vibration on the sub's box, it can color the sound from the speaker. Speaker manufacturers (like Axiom) go to great lengths to reduce or eliminate vibration to give their speakers added clarity. Whether it will be noticable in your case, is another story (perhaps the rubber feet can absorb the vibrations, or maybe you can put some acousticly inert material between sub and speaker to limit any coloration).
