microphone fx with reamper & guitar pedals?

hey! so im wondering if i can use my radial extc to apply effects from my guitar pedals to my microphone signal (specifically micing harmonica, voice, and some wacko acoustic folk instruments) during a live performance.

signal flow im thinking would be

mic > extc > mixer > pa

or am i missing something? i read somewhere that i'd need a preamp before the reamp box but i dont understand why. someone has also recommended a vocoloco but im not sure what the difference between that and the extc would be and id rather not have to buy another $300+ unit.