What are your opinion on fillers/Botox with melasma patients?

In general, injectables would not be expected to make melasma worse.  Melasma treatment typically involves medical therapy and, less commonly, laser.  In the event your skin is red or irritated from either of these treatments (or some other reason), I would wait until it returns to its baseline color before undergoing injections. 

Botox or filler injections should not impact or affect melasma, so you should have no problems if you'd like to have your frown lines treated. Melasma is typically influenced by a variety of other factors including sun exposure, hormonal changes (i.e. through pregnancy or oral contraceptive use), and genetics or family history.