Unless you have tried it, I don't see how it could work. The actuation ratio of a shimano D is around 1.7:1 versus 1.4:1 for old campy.... The overshifting will be considerable!
Why wouldnt it work??
There's no overshifting. The cable pull on the OP's campy shifters will match with a 8-speed campy cassette. The derailleur doesnt dictate the cable pull, the shifters do that.
For several years I used an 8-speed "600" derailleur with an otherwise all campy 8-speed drivetrain. The shifters were campy 'Syncro ll' DT indexed and were 8-speed. It shifted great, even through that Shimano derailleur until I traded with a forum member for his 8-speed Chorus derailleur.