@August44 - if the cause of the witches broom is genetic, then there's a better chance that it may be stable. Still not 100% , but somewhat better. The only way to know is to test it by propagating and growing it out.
Maybe your friends at the nursery will be interested. They could pay for the lift, and do the grafting. They could give you a grafted tree or two as a finder's fee. The nursery will have the time and space to test the broom for stability.
I don't think Douglas fir can be rooted from cuttings. I also don't know if they can be ait layered. A grafted tree is not necessarily disqualified from becoming bonsai. Well done grafts are allowed. 90% of all Japanese white pine in the USA are grafted. For some cultivars, grafting is the only propagation option.
See what your friends at the nursery say. Maybe they will be interested.