if the legs are firm and study that is all that matters, but if you intend to move the camera you need a good video head. They are making some less expensive fluid heads for smaller cameras like DSLRs. The problem you will run in to with a photo tripod is that a good video head is a ball type for easy and fast leveling and most photo tripods will not except them and you have to level with the legs.
But if you have something all ready and it does the job for you use it. It is really when you are buying new gear that you need to rethink what is most important for your current needs.
You can find tripod heads that are fluid heads that will work with photo style tripods. Look to the same manufacturer of your sticks as a starting point. Vendors like Adorama and BH carry a wide selection
Richard M. Harrington, PMP
Author: From Still to Motion, Video Made on a Mac, Photoshop for Video, Understanding Adobe Photoshop, Final Cut Studio On the Spot and Motion Graphics with Adobe Creative Suite 5 Studio Techniques