I read stories about workouts among the players, such as this one organized by Larry Fitzgerald and attended by Green Bay Packers WR Greg Jennings. But it's not like I hear about every player attending them. It's more of a story when someone like Jennings shows up.
LB A.J. Hawk said it was just a reason to get together with teammates, or friends in the case of Jennings. Which isn't really unusual because players often train together during the offseason. This article on rookie 6th round LB Ricky Elmore, who trained with Big Clay in preparation for the NFL draft, talks about how LB Clay Matthews trains a lot at the Proactive Sports Performance center in California. And I'm sure he happens to train with other NFL players while there, lockout or not.
Maybe we should be "waiting for the first ACL tear", but that's the case every offseason. You never know when a player might tear something lifting weights or playing in a pickup basketball game.