Grumpy is right. Radiowaves are not sent to particular points, but rather out everywhere. The radio just picks up what waves happen to be around it. As such, having a radio on does not increase your risk of being hit.
There are other factors here though. (all very minor!)
1st, metal aerial? That might increase your chances a bit.
2nd, rubber tyres. This decreases your chances a lot, but this might be negated if:
3rd, water over the metal wheel rims. As this then gives a reasonable connection. But that depends on how fast you're going, as if you're going fast, the water will be only droplets, and that doesn't work.
There might be more, I'm getting bored now...
So basically, no difference.