Welcome to this forum @David_White!
I happened to have a NI-USB6002 lying around. I guess that the 6008 is similar although I did not see it listed on the NI website, so assume it is an older model.
First, I downloaded and installed the NI-DAQmx software. That whole process reminded me why I never liked the NI stuff. The whole process took an hour or two. You can then check with the NI software that the device works and that you can change the digital output.
Then, start MM and select Devices > Hardware configuration. In step 2 find NI100x in the list (if the driver was not installed correctly, it will be greyed out), and select the DigitalIO device. Once your select that, there is a list with 3 properties. I did not really understand what I was asked to do here. What worked, was to use the dropdown menu in the first property and to select Dev1/port0, and then write that same string in the second property.
Once I had that, I could manipulate the “State” property of the NI device in MM. Setting it to 1 caused the output of pin 0 to (of port p0) to go hight (3.3V), setting it to low caused it to go to 0V.
I then went back into the Hardware Configuration Wizard, add the Utilities-State Device Shutter, saved the configuration, then added the group “System” with the NI device State property, and the State Device Shutter Shutter selected, set the State to 1, and the State Device Shutter to the NI device. That worked, and if I had your VMM-D4 shutter connected to the output of pin 0, and it responded to the 3.3V TTLs, it would have opened and closed when pressing the Shutter Open/Close button in MM.
I find the NI device to be pretty clunky (especially its software). A much cheaper (~$35?) and (as far as I can tell) fully functionally equivalent choice (from the point of view of Micro-Manager) is an Arduino. Also a bit of work to set up, but less than the NI USB board.
Hope this helps!