I would expect it to be commonly known.
The word may be more familiar to you than to most people, matt. I certainly had to look it up to see what it means - "(
transitive,
nautical) To unfasten (a hatch or door)" according to Wiktionary. Most of the online dictionaries don't even list it. And it doesn't seem to be in any of the Oxford dictionaries, even the full OED.
Still, the word is in Merriam-Webster and Wiktionary. And it is occasionally used, oddly enough, often in science fiction. For example in "The New Martian Way", a story by Brendan DuBois, published last year in
Analog magazine:
I wandered around to the storage shed, undogged the door, and with aid of my helmet headlight, peered in.
Undog will be accepted in future, but as a rare word. And so will
undogged and
undogging.
