[Keeper of Dol Guldur]

Well, Beorn was a man. Of course, but Luthien was an elf and she was daughter of a Maia. As a matter of fact, Melian was in elven form as queen of Doriath. Very powerful and beautiful and bright but in elven form no less. The Akhallabeth (did I spell it right?) said that when the Valar, the Ainur appeared they appeared in the form of the children of Illuvatar only greater, and more beautiful. Of course, Melko was some thirty feet tall and horrible to behold and Ulmo appeared big as a wave with shells and pearls adorning him, but of course the Maiar would be lesser in stature to these two greats. And of course, with Olorin traveling with the elves there is always the possibility of him having been in his true form or something along those lines (not Gandalf the old man form). Back then things weren't as hidden.

As for Radagast being master of many shapes and hues, the whole shape thing really points at something. Maybe he blessed the line of Beorn's forefathers. But no person can call the location of Beorn, Radagast and all there friends coincedence. Radagast definitely had some hand in the ancestral lines of Beorn, whether directly or indirectly. And Gwaihir was right around that area as well. . . As for Beorn's unbecoming speech of his "maybe" father ("not a bad fellow"), he was a bit standoffish towards Gandalf anyway, but it would make more sense if Radagast had blessed his lines, be them bear or man. Remember how Gandalf blessed old Barly's brew. Well it was the best year ever as far as the Pony's stock went.

Man-magic? I think the Numenoreans were a little above men. Even the nearby woodmen and the Rohirrim (the closest relatives to the Beornings) had no power like transfiguration. Dalelanders, Bardings, Esgarothians? Nope. Actually, the Numenoreans didn't either. Their magic was more in the form of prophecy, omen and strong blood lines. Beorn just had straight up magic, like Gandalf (or Radagast).

I'm really moving from Radagast the father to Radagast got helped by some bear in the woods (or man in the woods) and blessed his line.