Yes, you can use any fixture for the light. The only thing "special" about the ones at the pet store is that it has a hood to direct the light downward, but as long as you follow directions for how close the light needs to be, it doesn't really matter.
I actually recently used a cheap under counter mountable fixture from Walmart and rewired it to fit into a hooded aquarium light I had that stopped working. Was a PITA, but worked out great.