Can knowing an RN/LPN on a floor help get you a job?

The short answer is yes, it can help. The longer answer is that it really depends - how well that nurse is liked/valued, how much leeway the nurse manager has in hiring, how well that nurse knows you and how well or willing she is able to give you a glowing reference, how many internal applicants they have and how many other nurses on the floor have people who they are trying to also get the manager's attention about.

Most people in my department were hired off recommendations, including myself. You still have to be qualified and have the proper experience but sometimes it helps weed out the nut-jobs if someone they trust can vouch for you.

It may get you an interview. If a current employee comes to me about a friend, I will ask for a resume. If I like what I see on the resume, I will schedule an interview. If the person interviews well, then I will set up a peer interview with staff. Whether the candidate gets hired depends on the peer interview, as well as whether or not there are other candidates who might have done better in the interview process.

100% yes.
It's called networking.

At the last hospital I worked, I got the job through back avenues. It was complicated and the hurdles I had to jump made a funny story. Prior to getting that job I had submitted many applications online and received no calls back. Out of curiosity, I asked those in my hiring cohort how they obtained their positions and it turned out that EVERY single one (in a class of about 15-20) also had some unusual connection. We all agreed that the online process was a waste of time as everything apparently goes right into the trash bin. The funny thing is that I later heard my manager citing "lack of applications" among her problems in hiring more staff. It seems that there is a HUGE disconnect between HR and management.

It can help. It's no guarantee unless that nurse is also the hiring manager (and even then it's not 100%), but it is a big boost to your case.

ALWAYS use your connections. Of course it can help. Does it always? No. If your friend is the nurse who the manager hates then it won't help you but if your friend is a conscientious nurse who the manager trusts, it could easily land you an interview.

Yes, like others said. If the nurse you know has a good reputation and will speak for you... I think in most cases it would at least get your application/resume pulled from the abyss that is HR.

Worked for me.