What I have learned, and learn to trainees :
Identified means that you have performed an ICAO identification procedure (DOC4444) to get the correlation between a position on a surveillance display and the ID of that position
radar contact means that someone else have performed the identification process and with the help of an automated approved system,the link between position and ID is maintained on your display.You do'nt need to do again another identification process but saying "radar contact" inform the pilot that after the hand over the ATC radar service is still the same.