IF you have no takeoff penalty due to crosswind then it is likely that the cert testing demonstrated little or no need to use differential braking to maintain heading/centreline. In that case the effect of a wet runway on the takeoff crosswind limits should be negligible.
IF it was determined that differential braking was required then there SHOULD be some kind of lower limit on a wet runway to account for reduced steering capability from the brakes.
We always try to demonstrate Xwinds without diff braking.