That's a distinction with essentially no difference in this case. They're civilians working with/for the military in an armed conflict as armed personnel. There's less difference between the two at least as it applies to their case than there is distance between my butt cheeks.
And private military contractors are under the UCMJ and this has been the case since 2007. As far as I'm aware that hasn't changed.
Pardoning these guys absolutely 100% sends the message that our troops, in addition to other US personnel, aren't beholden to even our own laws let alone the laws of other countries and lives of their citizens.
https://www.brookings.edu/opinions/f...y%20operations.