Does tyre tread give better grip in the wet?

Counter-intuitive though it is, the answer is almost always: No!

At least this is the case on any surface where the tyre can make impression.

Unlike car tyres, the rounded profile of a bike tyre makes it almost impossible to hydroplane at cycling speeds. This means that the presence of a tread pattern can actually result in the tyre having less grip because the surface area in contact with the road surface is reduced.

Of course don't take my word for it. Do an internet search for slick vs. tread tyres and you'll see how deep this debate can get!