: So was Radagast responsible for all of those crows seen by the Fellowship in Hollin, or was that Saruman's doing alone, or did Radagast tell the crows to follow Saruman's orders?

I don't believe so. Aragorn was fairly convinced they were from the enemy but I doubt he knew which enemy. My guess is that they were spying out the land for Sauron. Saruman's spys seem to have been made up of mostly men and orcs. Concerning the last battle at the end of the SA it is stated that even the animals chose up sides. I'm assuming these crow like birds still held to their allegiance w/ Sauron's forces.