Tracy White is one of our two ST leaders, along with Slater. These two are good enough to be on the team without any expectation of them every getting a rep as a position player.
On the other hand, either Francis or Rivera will need to be able to contribute at a position.
Really we added Donta Hightower to our core LB of Mayo, Spikes, Ninkovich. In order to get all 4 on the field at once Ninkovich is seeing time at LE but he is was still are 3rd best defensive player last season play SLB. Tracy White saw some time as a coverage LB last season in the playoffs and was also solid.
Tarpinian is on PA and I am sure we will see him sooner rather then later and he brings a lot more upside then Carpenter with basically the same skill set.