Well, lets get the signal levels down first (from weakest to strongest)
1. Mic (LowZ)
2. Instrument (HiZ)
3. Line
4. Speaker
You want send a LowZ mic level signal through a processor that is designed to handle HiZ instrument level signals. Then send a wet instrument level signal to an input on your mixer looking for a LowZ mic level. It won't sound too good. It will probably be very noisy. When you send it through the mic pre it will only amplify the noise. Unless if you're going for something artsy with it, it probably won't turn out that great.
Heres my advice: Instead of running the pedal in series with your mic, run it through the aux send/return on your board. That way you can mix your wet signal with the dry. Then you won't be sending the effect through a mic preamp and on top of that you'll have more control over it. Record your vocals dry. Add the effect at mix down. -Joe