Yeah this works like you've described. Sometimes I play mono and sometimes I play stereo. The vocals are mixed with the guitar signal in the axe but if you were committed to playing mono guitar for all your gigs you could send the vocals to the left output and the guitar to the right so that the FOH could mix them separately.
The vocals are always the same level. The Fx Loop Block is always in default but you could change it per preset of course if you wanted to. I control the vocal level on the actual Mic pre which always stays the same. I make all my own patches from scratch so they are usually made to the same output level.
It's great to use an expression pedal to bring in a massive multi delay on the vocals. Also when the Axe Fx 2 came out they added more options for tuner muting. So now I can talk to the audience while tuning up where as before it muted all output on Ultra and Standard, Thanks Fractal!
Another thing that this sorta setup helps me to do is to send Synth Block drones, via the Fx Loop Block through the talkbox and back through the Axe FX for some delays etc.
Sounds like this....
I hope this helps.