I'd guess it would depend on what sub you're using. If it's a front or downward firing (and ported) woof, you shouldn't have a problem.
On the other hand, if you're running an SVS or other top ported sub, it might not be such a good idea.
The vibration might very well cause your dvd player to misread, at least it did on mine. What you can do is to get some Vibrapods (www.vibrapod.com ) ( about $6 each ) and put one under each corner of your dvd player. This worked like a champ for me plus it really increased the tonal qualities of my player. I thought these things were another bogus snake-oil tweak when I first decided to try them, but they really work.-----TJW