As to your question, generally, however: Yes, satellite radio can tell how many radios are tuned to a particular station at a particular time and utilize that data in making programming decisions.
As far as O&A on XM are concerned, however, that is a more or less moot point b/c their success on XM was judged on unique surcharge subscriptions.
Stern, on the other hand, was expected--and was HUGELY successful--at creating new Sirius subscriptions since Sirius does not employ the a la carte surcharge business marketing model.