I am looking at KMOT and I see a little dot over the airport symbol, is that the center of the VORTAC?
The dot in the center of the star means that there is a rotating beacon available on the airport from sunset to sunrise.
See the FAA Aeronautical Chart Users Guide Page 8.
The actual center of the VORTAC is the small dot between the runways:
Which you can find the description of in the chart users guide on page 8 as well: