John - it is only smart ELTs that might inhibit their 121.5 transmission in the presence of a 'dumb' PLB transmitting on the same frequency.
Your ELT will be 406 mHz with a 121.5 transmitter embedded as well - this is because you can't home to a 406 Mhz transmission very effectively as it only does a burst transmission every 50 seconds, unlike a 121.5 beacon which transmits continuously.
121.5 and 243.0 transmissions are not monitored by satellite any more - hence the move to 406 beacons which are.