At the press conference on Wednesday, Mike McCarthy was asked about S Aaron Rouse and he mentioned this about the safety position:
You'll see Jarrett Bush at some point start working back there too. There is a lot of talent back there.
Bush was the nickel back last season, and played opposite CB Al Harris on three receiver sets while CB Charles Woodson covered the slot receiver. Brian Carriveau thinks it's the beginning of the end for Bush.
In any case, it's possible that this might be the last opportunity for Bush to prove his worth to the defense. It may be weird to say that about only a third year player, especially one with a lot of athletic ability, but declining production and an infusion of young players could have Bush on the fence.
It's true that during practices this month I've read CB Tramon Williams and 2nd round pick CB Pat Lee's names frequently, but I can't recall a single mention of Bush. However, it might also be an indication that Lee and Williams need more time against the 1st team offense than Bush.
It might be that the coaches want better coverage from the safety position where S Atari Bigby and Nick Collins aren't the greatest in pass coverage. Maybe they are considering benching Bigby on passing downs and letting Bush play safety. Maybe Bush's roster spot is in jeopardy, but at this point in the offseason it's too early to tell.