There must be guidelines somewhere. Otherwise, if I was running a team, I'd sign people to $1 million guaranteed and a ton of easy incentives.
You could give a mil for showing up at camp. A mil for making the team. A mil for playing in each game, etc.
Making the base $1 million and the cap hit insignificant.
JPP had snap incentives when he returned in 2015. Cruz had some additional per game roster bonuses that he was able to earn. But in Cruz's case, those were not-likely to be earned since he missed all of 2015.
Also, if you have performance based incentives (e.g. sacks, catches, INTs), you could get players taking unnecessary gambles to try and achieve those milestones, especially later in the year.