In a situation where an admin will enter sensitive information into a keyboard (the root password), what is the risk that a bluetooth keyboard (ship by default with Mac systems these days) would put those passwords at risk?

Another way of asking would be: what security and encryption protocols are used, if any, to establish a bluetooth connection between a keyboard and host system?

Edit: Final Summary

All answers are excellent. I accepted that which links to the most directly applicable information however I also encourage you to read Nathan Adams's response and discussion about security trade-offs.