If the broody is vaccinated. Then what? Do you let her stay with the chicks and vaccinate the chicks or separate the chicks and vaccinate them? None of the articles have addressed that. It is sad that you can no longer let hens hatch chicks because you wouldn't know if they were exposed to Mareks or not if they had the vaccine. Taking them away from the hen would be awful. I would rather a natural hatch than an incubated one any day.
Unless you know for certain mareks is in your flock, which takes having birds with the symptoms, sending the bird to be tested, which requires tissue samples and a vet visually looking at the sciatic nerve among other things then a diagnosis- I don't think you need to worry about it. To answer your question about the vaccinated broody- you can vaccinate the chicks and let the broody raise them. The quarantine time mentioned is for when you know mareks is in your flock. Vaccinated chicks can't be exposed to the mareks virus for a certain length of time because the vaccine won't work and then again the vaccine is only to help prevent mareks fatalities. Honestly, I wouldn't worry about. Take good bio security measurements, keep a closed flock, don't let other people that keep birds walk around in your coop and yard. There's only so much you can do. It can be carried in by wild birds, you can pick it up on your shoes at the feed store-basically anywhere- it can live outside the host for at least a year in the dirt and dust- it is air borne and is transmitted through dander. Once it's in your flock you basically have two choices-cull all your birds and wait at least a year before keeping birds again or wait and see which ones make it. The latter can be a long drawn out process that is painful to watch as your flock dies off. It's is best to euthanize when you see symptoms.