For the record, according to A Guide to Middle-Earth
by Robert Foster, Radagast is mentioned (and I have checked and confirmed):
- On pages 336-337, 342, and 359 of The Fellowship of the Ring (1970's Ballantine edition)
- On page 121 of The Hobbit (again, 1970's Ballantine edition)
Though assuredly a minor character, a far cry from only mention on one line.
Any word of the Blue Wizards being in the film?