Yes, people have been known to rank their pre-lims after all their PM&R programs in the event they don't match somewhere. However, keep in mind if that is the case you won't be able to SOAP into any categorical positions (whether PM&R or if your second choice would've been say, psych or OB-Gyn if you had to SOAP into something else). I do believe you can still SOAP into advanced positions--as J4Pac mentions, ask the NRMP about it.
The odds are quite low to match into PM&R if you don't match the first time, but there are people who decide not to do go their PGY2 year and PM&R positions can and do open up. So it isn't unheard of for a few people to get a second chance. And occasionally not every PM&R position fills (I think last year there was one unfilled spot? I can't remember)
For this reason I did not rank any pre-lims after PM&R programs on my main rank list. I figured if I didn't match, I'd SOAP into an FM or psych program. (However, I also felt I ranked more than enough programs to match, including my home program that I was 95% certain I'd have matched into if I went that far down on my list, so I figured the odds of SOAPing were pretty low anyway)