I need to make a cut for the body mesh that matches the vertices of the white mesh that are closest to the body so I can get more accurate weight painting with less clipping/deformation, but I’ve tried for many days and have been unable to figure out anything on cutting a mesh to match an exact set of vertices.
Welcome 
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…boolean operation is the keyword… for example with a boolean modifier… to “see” something the other mesh should be set to Viewport Display: Wire…
And maybe you have to extrude it somehow… so make a copy of it…
…it’s always good to say what someone tried before and how to make understanding task clearer…
As i said: you might have to copy the object and make some tweeks… (extrude ?)… maybe even divide it into several parts… because the boolean operation is not so easy as it might seem… therefore the different options…
This for example doesn’t work if you use Exact without Hole Tolerant…
And for examples it’s alwasy good to have some overlapping volume to cut from and out…