Impedance / bandpass
Many devices offer low output impedance compared to the load.This is simply to allow for ex a mic to be able to be split to the FOH console and the monitor console without degradation in performance. We often see 200 ohm rated outputs on preamps / digital signal processors etc , what it means is that you can feed 3 600 ohm input amplifiers in parallel without signal degradation.
So .. if the output of a device has lower impedance than the load you're always ok .We are not talking about level , simply impedance here . As to connecting ex Shure SM-58 etc to transceivers , one of the things i'd be concerned is not level which can be compensated as required easily , it's bandwidth of the RF signal you transmit with the larger audio bandwidth. If you want to keep in line with the FCC guidelines for that spec i am certain that you will have to use a lowpass filter in the audio chain.