Yeah, I think I got it after you posted what Fewell said.
I think the Bills want to see if Crowell can play the SLB spot because they want him there so as to be able to cover the TE. And as you said, since Spikes has played SLB in the past, if Crowell CAN'T play SLB, he'll probably play WLB with Spikes moving to SLB. But the most ideal situation is Spikes at WLB and Crowell at SLB. I think.