I've been using the storm charger as my overnight charger since I got the DX. Works fine. It will just charge a little slower. Nothing I'd be concerned about.
The best charger to use will always be the OEM charger plugged into the wall, anything that charges slower or faster than the original ie: USB or chargers for other devices can have adverse affects or just not give you a proper charge
I recall reading on moto's site that this is a special charger that is designed to charge the Droid X faster. I compared the charger to one of my other universal verizon charges (from an LG), and did confirm from the specs that the moto charger feeds a little more juice.