For 8S cassettes:
Campy: NO, not compatible with Shimano cassettes
Mavic: Maybe, some had a screwy spline pattern which means a Shimano cassette will not fit.
For 8s freewheels (yes, there is such a thing):
will work with either Mavic or Campy threaded hubs. This is NOT recommended because the axle needs to really long for 8s and gets very weak and prone to bending,