I’m a brand new helix/headrush frfr user.
It sounds to me like you’re thinking about this way too hard :).
The FRFR speaker/amp are the best way to reproduce and deliver a modeler’s tone. It essentially, they’re no different than what your regular amp would do.
So yes, you can use it just like an amp. All that matters is that you’re happy with the tone you’re getting.
I gigged my helix last week with a crappy little “FRFR” speaker (I only got the headrush a day later alas), it was a small club that doesn’t mix and mix instruments in the PA, so I used it just like an amp. It worked super well.
Connecting a FRFR speaker (or helix directly) to the FOH is really just a bonus. But it’s really the same thing as mic’ing the amp to the FOH. Except your tone is already going through an FRFR system so no need for mics or any other “conversion tool”.