Sve,
PUP is a preseason designation, it only applies to the preseason, once the regular season starts its just called season ending IR, there is no 6 to 8 Weeks IR, thats the Reserve PUP or IR/PUP that you can apply to players who never participated in training camp practices.
As for the preseason PUP, there are two different PUP's, one is the "Active PUP", so even if the player has not competed in practice, you are still designating him as an active player, therefore there is no roster exemption for that player. Until a few days ago that applied to Devin Smith, he was PUP, but he was "Active PUP". It was only a few days ago that he was officially moved from the "Active PUP" to the "Injured PUP", aka the IR/PUP, and thats the one that gives you a roster exemption for his spot, but now (unlike Active PUP's) he is no longer eligible to return until after six weeks.
Breno, OTOH, is still on the "Active PUP", so he is eligible to start practicing or playing at any time, even week one if he's ready, but there is no roster exemption for Breno ... unless he, like Devin, is moved to the "Reserve PUP", then you get a roster exemption, but then he is ineligible to return until after six weeks.