OF COURSE!!!
Dude, the more light, the merrier.

If you're flowering with one 1,000W HPS, and you add a second 1,000HPS, buds will be bigger.

If you have a 1,000W HPS for flowering, and you add a second 1,000W MH, buds will also be bigger.

The question is, which option would be better?
HPS + HPS
or
HPS + MH
?????

But dude, if you've got the bulbs, plug them IN!!!!