Exactly, and that's the key issue.
Bobby Carpenter should be able to play either ILB or OLB, and that's one of the many reasons I'd like the Pats to take him in round 1. He's primarily an OLB, but has the size and ability to also play ILB (a lot like Vrabel, whom he works out with).
They could also likely pick up Kai Parham in day 2 as a run stuffing ILB, as his stock has been plummetting due to slow 40 times (but, speed isn't nearly as important for a 3-4 ILB as it is for a 4-3 MLB). Add to that picking up Ryan LaCasse, a very speedy DE OLB tweener with great size as a developmental OLB project, and I'd be quite happy.