I wonder.
The whole process is very clouded in secrecy. I think any strict statement of yes vs no for any question relating to the process is questionable. Perhaps USUHS students don't get explicit preference, but it can't hurt that they get earlier and more frequent face-time with the people who make decisions on who gets selected.
I have run into a number of USUHS students who have been involved in research with milmed docs at the major MTFs for years before they applied. Certainly these students get a leg-up over the average HPSP student trapped in Indiana, with no access to the program directors at Bethesda and San Diego.
Then there is the alma mater factor. A significant portion of the milmed lifers came out of USUHS. They chat with students about faculty, how it was "back in the old days", changes in the program. The average kid from University of Texas tends to be conspicuously absent from these conversations.