Outside of telling you that Radames is the Egyptian lover of Aida in Verdi's opera of the same name, I haven't been able to find any meaning for the name. I suspect the name probably has something to do with the Egyptian sun-god Ra, as a lot of ancient Egyptian names had the Ra-element in them.
Or perhaps the opera's librettist, Auguste Mariette, simply made up the name. While the story is supposed to have some basis in the Hellenistic *Aethiopica* of Heliodorus, others claim that it was an original work of Mariette's.
-- Nanaea