So I am speaking from personal experience.
Regardless of military service or not, HR's (Human Remains) are not considered "Freight". Throughout the air freight industry, HR's are handled with utmost respect.
Furthermore, everything that goes into the airplane has a priority:
1) Passengers
2) Luggage
3) HR's
4) Mail
5) Freight
6) COMAT (Company Materials)
Why is this important? During Christmas season there's tons more mail in the air than any other time of the year. All those cards and gifts! Plus people carry more luggage with winter clothing and more gifts. When planes are full, what do you think get's bumped? (left behind)
Starting with COMAT, the lower priority stuff gets bumped. I have never seen an HR left behind.
HR's are not FREIGHT.
Thank you for the first hand experience. I am certain that any employee who knows they are military remains treats them with respect.