Hatching eggs won't carry Marek's disease, except if they are contaminated on the outside of the egg shells.  Mycoplasma, however, can be transmitted to embryos inside the eggs.
And i think it's wise to have chicks vaccinated against marek's disease, in case it ever arrives in the flock.
Here, chicks raised from our own birds are not vaccinated, and any chicks bought from hatcheries are vaccinated there, and isolated long enough to develop immunity.  So, if this disease ever arrives here, our unvaccinated birds will be the 'canaries in the coal mine', developing Marek's related illnesses first.  So far, this has not happened, and I necropsy every bird who dies not related to predation.
Mary