I don't know about their program--I just never had any interest in going to St Louis so I never even looked into their program, but what I do know is there are a lot of PM&R programs that are far stronger than their name would suggest, and there are a lot of PM&R programs that are not as good as (sometimes nowhere near as good as) their name would suggest.
In general, I think the affiliation with a top-tier medical school doesn't have a a very strong correlation to the quality of the program--at least not as much as most other residency programs (though this is even more the case with EM and FM, which tend to be strongest when they're unopposed programs).
University of Washington, RIC (Northwestern), Mayo, Spaulding (Harvard), and UofM are all very highly regarded (ie., the top) PM&R programs at very highly regarded medical schools. But there are an at least equal number of PM&R programs at just as reputable of medical schools with programs that range from sub-par to just above average.
Is this a curiosity question? Because based on your username I'm assuming you're applying to/matched into derm.