There is only one way to do this using tool compensation. I have no idea if cabinet vision is capable of it nor how to turn it on, but the CAM program must be able to output the GCode with tool compensation for it to work.
Once you have enabled tool compensation in your CAM program, you can use Mach3's Tool Table to input the diameter of the tool. Note that Diameter Wear and Height Wear are not implemented yet, AFAIK it won't be until revision 4 is released.
The reason the CAM package must be compatible is because Mach3 needs to know what direction to apply the offset in. It accomplishes this by using left and right compensation indicators in the GCode (G41 and G42), always with respect to the direction of the cut (ie with respect to the tool). The alternative is adding the compensation by hand - but this isn't recommended as you need a lead-in move for Mach3 to properly determine the offset direction, and it can be a pretty painful process for anything but a very simple part.
Hope this helps a bit.