Can I hook this up to the m12 Milwaukee grinder? I'm wondering if this combination would make sense to make relatively clean drywall cuts.

Grinder's are notoriously bad for dust collection, especially when using in a "slicing" motion, which you'd be doing to cut out drywall.You'd be better off using a dedicated drywall cut out tool. Makita makes one with great dust collection.https://www.toolnut.com/makita-xds01z-18v-lxt-lithium-ion-cordless-cut-out-saw-tool-only.html