I run both MH and HPS for flowering. By all means.

The MH, while not the proper spectrum, still serves a purpose by bombarding your plants with UV-B rays. (HPS emits none).

A lot has been learned by studying the potency of plants grown at higher elevations where the UV rays are strongest.

It is theorized the Plants produce more resin to absorb and protect the flowers from this harmful radiation. Ideally, the HPS : MH ratio is 2:1

But keeping them both burning is absolutely the ideal scenario. The HPS still gives the flowers / fruits the red waves they need.