If the ProVoice system is running ESK, then yes, it would be a big waste of money to purchase a ProVoice portable.
However....
One can conventionally scan the repeater outputs and monitor ProVoice traffic, but this is no different than the days w/o trunktrackers.
However.........
One can use the ESK enabled version of etrunker to control a radio that provides a 10.7 MHz IF output, which can be upconverted using a mini-circuits mixer and a signal generator, fed to a ProVoice radio sitting on a single conventional channel.