Like wtp says, try it. I would say it depends on what you want to listen to. If, like reedeb says, what you desire to hear is fairly strong, some sort of trunked or repeater system, or not afar, it should fit the bill.
The same goes with listening to FM broadcast. Instead of getting a splitter, see if you can receive the FM stations you want with a foot or so of wire on the dash or in the rear window. I once used the car antenna for scanning, and a 6" NMO antenna mounted inside a rear window for FM (didn't get AM well, but I never listened to AM anyway) and it got the FM stations I wanted full quieting.