Do we ever need more than three OLB's active, except perhaps when pass-rushing Jarvis Green isn't playing? Woods is our #3 OLB and is a top Ster in addition. Unless there are health issues, I don't see Crable ever being active.
BTW, there is even less need for ILB backups, since there is often only one ILB on the field. Mayo has been playing every down. However, there should be some reps for the #3 ILB. Alexander, the backup has been injured. Guyton may be getting some reps, or Pioli will be on speed dial to a certain ILB.
The bottom line is that we have 9 LB's: 4 OLB, 4 ILB and Izzo. If the #3's and #4's are to be active, they need to be solid special teamers. Woods, Alexander and Guyton qualfy, giving us 8 active LB's, 7 since Alexander is injured. Note that the replacement on Game Day for Alexander needs to be a STer, hence the signing of Eckel.