The races will be done by a combination of Motor Racing Network (MRN, owned by NASCAR), Performance Racing Network (PRN, at Speedway Motorsports tracks, except for Craftsman Truck series, which will be on MRN) and the Indianapolis racetrack's own in-house radio network (IRN).
Sirius Speedway is done by MRN and I'm gathering that the other shows are, too. I did see that the only traditional broadcast MRN show that's on Sirius (other than the races) is NASCAR Live with Eli Gold (7pm Eastern, Tuesdays).
So it's likely that there are rights issues... and the contract between Sirius and MRN may not allow streaming.