I think your point on searching more for thermal printer threads may be the way to go in this circumstance, as it appears that I'm not able to get the MX64 to do anything particular that would help with this.
As for the printer drivers, those were already installed on the server. More recent sessions have been showing the printer to appear as redirected, but the printer's queue gets stuck.
I tried a different solution, for the sake of testing, where I installed the printer on the server as a shared printer from the client, but it seems that the RD session refuses to list any shared printers at all. Not sure if that's a RD feature or a GP issue--have to look that up. FYI: This was done during a single VPN session so as to not lose the client's address for the share.
Now that I see MS RD services won't list shared printers (unless I find otherwise), the point of having the MX use an assigned or reserved IP address is moot here.
I have a feeling that this may end up boiling down to printing a PDF to client desktop, then print that to thermal.
Came to my senses and remembered that shared printer installations are per user, which means setting this up as admin was the reason for it not working. Just tested and got a successful print to a shared Zebra (not redirected) over RDP.
So I'm right back to my original need for establishing a static address mapping to a VPN client. The only thing I can think of is to set the client pool to 1 address only. This of course means only one client can access at a time. 😞 I'm starting to like the Z3 idea.