Yes they can be on light. The only concern about it is algal growth, specially in gorgs. But if you can control this there's no problem, in fact mine are under MH 10 hours/day. Keeping a good part of the for years now.
Keep in mind that NPS require a good amount of food, so maintining water quality is more difficult and hence the more light available the more chances for algae to develop. Also some nonphoto LPS (such as tubastrea)when they first arrive from shop to the tank they tend to open without light, so they only feed at night time.
Regards