The names surrounding Wolfgang in the credits are mostly vampires, with some humans. The name Atilla is apparently a Turkish variant of the Hungarian name Attila. Since Underworld was filmed in Hungary, I wonder if the actor’s name is misspelled: it’s possible that his name is Attila Pinke. He may be a Hungarian who had a non-speaking role, like Sándor Bolla, who played Rigel, and Judit Kuchta, who played Zsusza.
Is there a picture of the actor or the character? The Underworld Wiki speculates that the character could actually be Duncan, a vampire who spoke no lines and was never named in the film. The novelization lists his name as Duncan, but perhaps he was intended to be named Wolfgang in the film. The novelization does not mention anyone named Wolfgang.
I can’t find an official script of Underworld, but the transcripts I’ve found make no mention of “Wolfgang” or “Duncan”.