In general, I wouldn't suggest mixing them for anything longer than short-term storage and expect to get the effects of both. Glut has fairly specific pH requirements to be stable in storage, and even then it does break down over time. I doubt that Flourish has the right pH.
Mixing a small amount of glut into micronutrient mixes to prevent mold growth is fine, it shouldn't harm the micros... However I wouldn't count on this as a mechanism for dosing glut, as the glut will probably degrade faster than normal.
If you really want an authoritative answer, ask Seachem... They are generally pretty good about getting back to you in a few working days.