The Campagnolo Veloce is a ten speed shifter and the Shimano is also ten speed derailleur, so can a shifter be compatible with another brand derailleur, specifically Campagnolo and Shimano?
Not without modifications, because the amount of cable pulled for shifting a single cog is different. If you have to make the combination work, there are hacks such as ShiftMate adapters and Hubbub cable routing that can make it work.
Other thing to consider is that 10-speed cassettes from these two brands are slightly different width, so for best function all three should match.
Advanced indexing techniques Campag Ergopower shifters
You can use these 'drop handlebar' shifters with Campag or Shimano-compatible rear mechs by swapping an internal ratchet, as follows. The table shows which cassettes work with different combinations of Ergopower shifters and rear mechs. For example, 'Shim 8' means 'use a Shimano-compatible 8 speed cassette'.
mod 4 : pitch of mech modified by turning its anchor-plate by 90° - method 4 below x : non-standard pitch - respace your cassette with Highpath spacers