Dan I have an inlaw who is a framer who built his own house, pear & beam with concrete skits enclosing the bottom. Same as your dads.
He did not put any vents in the skirts AT ALL. He would not listen to me to vent the foundation. He also did not want cold air under his house.
The house rotted from under him. This is serious, not just a little mold.
The kitchen floor are was the first to go but he said for years he had a leak in the wall. Doors thoughout the house started to hang up. Humidity was always high in the house......
I even offered to put the vents in and install a fan to insure proper venting. He wouldn't hear of it.
Today after tearing down his house he built another one next to it. This time with a very vented foundation.
If anyting I would try restricting some of the air, not total blockage. I am not in a cold climate.