There are a good amount of people (including myself) that use a double fixture and have a 5.0 reptisun and grow light in the same fixture.
One thing to note is that the "grow lights" are usually useless and are just made to make the plants look better, not for actual growth.
What i've read is that you want a bulb around 6500k and that the aquarium/plant lights are good for promoting plant growth.