To my knowledge, since being declared 100% after his 2005 shoulder surgery, Drew Brees has never missed a down for the Saints due to injury: http://www.nola.com/saints/index.ssf/2014/08/drew_brees_misses_scrimmage_wi.html#incart_2box
Nobody is ever allowed to hit Brees in practice. Ever. Hence the red jerseys. For that matter I don't think any teams allow live hits to QB's in practice, do they?