If we drafted the best available LB or CB in the 1st round....
I think if either CB is taken (my preference is Cromartie, followed by McKelvin and then Jenkins) I think they have a great shot at starting some point in the season. Possibly not right away, but I think any of them can come in and be our nickle right away.
As for Rivers, I am not a big fan. I just don't know if he is going to be a productive NFL linebacker. I think he could possibly come in and push Shanle on the weak side, but then again I don't know if he is much better than Shanle (I admit he has more speed and range than him though).
Personally I am hoping for Cromartie. I think he has all the skills needed to be an impact player in the NFL. We desperately need a good, young CB and I think he is the best available.