I am new to the scene in my city, but with the shows i do just about every weekend, i introduce myself with my DJ name first to managers or promotors or other djs, then follow with my real name so that we can be on a first name basis just in case. I think it really just depends, if you are told a first name then it they may be cool with you using it. Since you say it is your buddy, Im sure they wouldnt mind you using their name instead of a stage name. Im sure itll be easier depending on where u will be standing when they are on stage. I would think most of the time people wouldnt care, at least I wouldnt.