Theres a chance it will work, the o/p of the guitar pickup and a condenser mic probably arent that far apart, assuming it is a condenser mic.
You'd need a decoupling cap, say 1u from the pickup to the xmitter, as condenser mic's are dc powered.
And you'll need a attenuator at the rx end, depending on what o/p it has, if it drives a speaker then you will need an attenuator, a 1k pot might do the trick.
Guitar pickup impedances tend to be low, as are loudspeaker outputs so I dont think you'll need to match impedances, you only need to do that if your going from high impedance to low, or if your operating at radio freq's.