sheel, yes they can directly get greencard but for that they have to wait for long time. atleast today they have to wait in backlog. may be they will change the rule later but for now if you are only
RN  and dont have BSN in nursing , then you dont have any option rather than waitng for backloged visa numbers.

if you have BSN you can atleast apply for h1b(h1b requires 16 yrs of education)