If I'm not mistaken, Mister Postman uses solely MH on his grows. Besides, you'd want the blue spectrum for the veg stage anyway. Grow on, brother
You can and you will see great growth in Vegatative stage but a small reduced amount during flowering. They always said a MH is best for Veg and a HPS is best for Flowering and USUALLY people that are only going to use one light go with the HPS for the entire grow.