It just makes sense to stock the PS with corners. They should have picked up a bunch of udfa corners, given Samuel's contract situation and Gay's injury history. Samuel and Gay are both free agents. The Pats should be doing everything possible to develop a fourth corner with some experience in the system for next season. Obviously a long shot, but with the OL and DL so young and deep, DB (and LB) are the spots to focus. I don't think there is any necessary link to the roster now, or Samuel's condition.
Also at center, the Pats haven't had a true back-up center for a couple seasons. Hochstein is a good guard, and an adequate center. Having a true center developing on the roster, maybe to replace him next year, makes all sorts of sense.
With Light, Kaczur, O'Callaghan, and Britt at tackle, it makes no sense to hold a PS spot there. Similarly, with Mankins, Neal, Hochstein, and Yates, there's not much room for a guard. Same story at DL - with Le Kevin and Kareem and the other young back-ups, there is little chance a guy like Zach West can make it.
Then again, the Pats are really rotating players through this season. These two are probably in for a one-week PS audition, and are very likely to be gone in another week. Possibly for another corner/center/or LB combo.