In all my years of listening to railroads, i've never heard RR police on the frequencies listed for them. I have heard them on the local road channels, though. That may be your best bet to hear any railroad police traffic.
In Florida, it wouldn't suprise me if CSX's RR police had a talkgroup on the SLERS system, but I don't know for sure if they do.
I have heard the NS police on the AAR frequency designated for them in the Atlanta area once. It was a crew calling them after another train saw some kids playing around the end of a train that was stopped in a siding. I've always assumed that's all they use those frequencies for (crews calling the police), and that they are not used for routine communications.