Well I never thought id say this but, I dont think you should unless you plan on going sps. There is no reason I can see to run MH lights on a prodomanetly fish only tank. Several reasons come to mind. First and formost is heat. Heat is a killer. There is no reason to deal with the heat unless you need to. Second is the electric. MH's will cost you more to run than your vho's.
Im sure its not news that im a MH person. I swear by them. BUT! There is no way on this green earth id be running them if I wasnt trying to keep sps. As a matter of fact LPS corals have been catching my eye lately and who knows, It may not be to long before I drop out of the sps farming and go full LPS. If that happens Ill run VHO's.