Troubleshooting a networked MFP

Does your firewall allow LPR (or whatever printing protocol you're using) to pass through?

I'm being told that the VPN tunnel is wide open on both ends allowing all traffic through.

if you can connect via web services, that goes via HTTP.
Have you tried using WSD printing?
The TCP/IP port may be failing due to latency, also some printers use SNMP over TCP/IP, which is often blocked.
Have you tried using an IPP port?

have you tried adding it by the hostname instead of just the IP?

I'm assuming your adding by creating a new port and using the "standard TCP/IP Port"?

is your local IP the same as the VPN ip's?

From my workstation which is a windows 7 box. I added the printer by using the "Add Printer" function form within Devices & Printers. Selected a networked printer > The Printer isn't listed > Add a printer using a TCP/IP address or hostname > enter the IP address of the remote printer. It connected and I can successfully send test pages to the remote printer. Looking at the properties of this printer under the hardware tab it has the pirinter listed as a system device and it has WSD print device listed as well.

When I attempt these steps from any other workstation in my home office I get a window indicating that the printer cannot be found and to make sure it is powered on.

I tried adding the printer via the local printer option as opposed to the network printer option and I get the same failed results.

The IP address of the remote printer is the same in the local office as it is in the home office.

When I try telneting to the printer I get a username prompt. I am able to login and access the device. If I try and telnet to the remote printer from my workstation in the home office on ports 515 or 9100 it appears to connect. I get a flashing cursor no failed to connect or connection refused message from the printer. Just a blinking cursor. In the past I have been told that is a sign that you are able to pass through the firewall and talk to the device on that specific port. If that is correct then it appears ports 515 & 9100 are open.

I would try changing what your IP scheme is at your home office.  

for example,
at home 192.168.0.1-192.168.0.255
at work 192.168.1.1-192.168.1.255

depending on the VPN you might have enabled a split tunnel. This means both your local network and the remote network are available to you and when you try to access that printer, the OS is only searching for it on your local network but not on the remote. Try disabling split tunnel, I guess you'll find guides how to do that according to your software used on the net. Unfortunately, with split tunnel disabled, you'll loose your local network resources like maybe NAS or local printer.