My class has several students in it who were nurses and I have interviewed a couple applicants who were nurses (or other licensed health professionals). Of those that I interviewed, I never held it against them. However, you can almost guarantee getting some version of the question, "why do you want to switch from nursing to medicine?" This has to be a really good and honest response; if it's not, the interviewer will smell it a mile away and hold it against you ("I want to be in charge" = bad answer).
While I cannot speak for all schools and healthcare markets, I am not sure if the "nursing shortage" is really a factor in many areas currently. Facilities may be understaffed, but for a relatively long time, hospitals in many cities all across the nation have not been hiring or only posting a few openings (I did research on this because my wife is a nurse and I just finished residency interviews). Obviously, this is due to the current economic crisis. Also, many nursing graduates leave the field for many different reasons, so why couldn't one of them be to become a doctor.
If you really want to be a physician, go for it.
-senior medical student / admissions committee interviewer