First all, what Reason version are you using? I hope any after R6/7.. That is the easier way of doing things.
In any case, selecting a vocoder and just randomly mic checking wont help.. The vocoder doesnt have direct mic or audio capability's. You'd have to route the source to it first. So, where do you get the source from?
Easiest thing to do is just create and audio track and select your mic as the input source, this will allow reason to directly get your usb input into the given audio channel, which in turn will give you routing capabilities. Get an audio splitter, route one wire to the vocodor, leave the other one routed to the audio channel's output so you have a raw source in your mixer aswell, just for vanity sake.
That outta work.
In version 5 (which has built in audio recorders in the sample devices (nn19, nnxt, redrum, kong..) you'd have to record it as a sample in one of the devices first. Clean it up (set starting marker etc), create a midi note so the sample will play and then route the device that plays it trough the vocoder.
In any way, see if you can record your raw input anyhow. Thats step 1 in the problem elimination proces.