Mirthcard-after reviewing the roster of PCs and the special qualities of the Dunadein and elves, it seems a little odd that Radagast, an Istari would have lesser racial abilities than the others. And to be honest I was unsure that anyone would take on Radagast.
So if you want, you could apply the celestial template or take the aasimar race for Radagast. They have an ECL of +2 and +1 respectively, so its up to you. Aasimar seems a good fit given the bonuses to search and listen and the ability to cast light, to say nothing of the resistences.If you choose aasimar the favored class can be changed to sorcerer.
Just throwing it out there.