I think just the opposite: get an absorbent, “dry” type grip.
Most grips and overgrips are made to be tacky, which works well for most players. However, if you sweat a lot, that tacky layer seems (to me, anyway) to force sweat to “pool up” on it and not be absorbed away from your hands. A “dry” grip will absorb the sweat better, letting you hands stay dry.
Also, try rosin bags or a number of other products available to help with sweaty hands.