Sure you can. You can veg under a MH, HPS, CFL independently or any combination you find best to fit your needs. I don't know too much about CFL as I don't grow with them. But I do not think 100w will be sufficient for the 8 plants it looks like you are vegging, so combining your lights should help. Running your hps 18-24hrs/day will be more expensive than if you had sufficient cfl. But you should grow more robust plants.