The antennas are different. They may work if you swap them but drop-outs may be significantly higher. Sirius is heavily based on satellite reception while XM is heavily based on terrestrial reception. The antennas are tuned to receive their preferred mode of transmission.

Also, when the FCC provided licensing for both companies, their bandwidth was not separated with a buffer frequency. Earlier antennas and tuners both have filters that reject the opposite signal to reduce or prevent cross talk.

So in short, you can't hurt the tuner if you try it. It may work, it may not. In order to get the best possible signal, use the right antenna.