I don't believe that to be the case for PM&R since Radiation Oncology is an extremely competitive field, yet there are quite a few students who go without really knowing its existence.
I definitely believe that PM&R is actually a DO friendly field. For instance, lets compare the field to radiology.
http://www.nrmp.org/wp-content/uploads/2014/09/Charting-Outcomes-2014-Final.pdf
On chart 3, page 5 - They show that PM&R has an 89% match rate for U.S. seniors and 53% for independent applicants versus radiology which is 99% of U.S. seniors and 70% of independent applicants. So overall PM&R is more competitive to get into than Radiology.
http://www.nrmp.org/wp-content/uploads/2014/09/PD-Survey-Report-2014.pdf
On page 95 of the 2014 NRMP Director's Survey, it shows that 97% of programs interview/rank DO students for PM&R, but on page 121 for Radiology 64% of programs interview/rank DO students. This is one of the few ACGME fields where DOs are interviewed and ranks in almost all programs. In 2015, 3 total were left unfilled in PM&R, but 150 were left unfilled in Radiology.
With that all said, DOs have hit top tier places in PM&R such as Spaulding hospital and Mayo Clinic (Rochester). However, the same can't be said for Radiology. Based on the data it is definitely a DO friendly field.