I use samba/nfs shares on my unraid server. You can find it I think under the tools tab.

Once enable you literally just map the share inside windows. I am doing exactly what you want to do.

Also using the vm on unraid your share is going through the virtual NIC so you should get faster speeds than what your physical unraid NIC has. But that won’t help you, just informative.

I don't see anything about Samba or NFS under my Tools tab in unRAID, but your comment triggered something to work in my brain. :)
I already had access to the shares via the virtual NIC, since I could see the unRAID shares by browsing the network from within the VM. All I had to do was map the one I wanted as a drive, and bingo!

The answer was in my question all along. Thanks for the push that got me over my mental speedbump. ;)

When creating a vm there’s an option to mount shares. I think it ends up working like a network share. Just edit your vm, it should be after the vdisk settings.

I’ve only ever had this work with Linux/BSD vm’s. OP is using Windows. If this does actually work for Windows VM’s, then I’d be so excited.

Hmm...nope. I don't see any options about mounting shares. Mine goes from Primary vDisk location to Graphics card/VNC settings, to Sound card, to Network stuff. Maybe it's an option to add a custom field or something?

In any case, my issue is resolved. I was able to browse the virtual network and map my share as a drive letter, which serves my purposes just fine.

Thanks for the comments, though! This is a very helpful and responsive community. :)