First, I'm obligated to say Wineskin isn't supported here. Only pure
vanilla Wine is, which is compile yourself and use command line on OSX.
You should try Wine version 1.2.3 or 1.3.14 and older to see if there is a
difference, since there has been some changes going on with the mouse and
pointers from 1.3.15+ that can be problematic.
You could also try Screen Options->Override->Fullscreen and/or virtual
desktop window, all of which use a Wine virtual desktop, and see if the mouse
handles differently.
Also check in game to see if there are any Software/Hardware mouse options you
can try.