It may not be. However it is being done every single day with zero drama. Unfortunately we are not allowed to post how to do it here because of it angering other members and moderators.
Defense contracts require a whole bunch of hoops to go through in order to cross into and out of other countries. It is a whole different set of rules than the average citizen. Even before COVID military contracts performed by non military personnel were a nightmare. I have been on both sides of it and I can only imagine the difficulty of the logistics during COVID guidelines.
Your posts are being deleted not because you are exceptional in angering other people, it's because we have clearly stated rules that you frequently do not follow.
Note that AvGeek and I generally let your posts which are not factually correct stand. For example, I did not delete your post above, yet. . . .
As for being a civilian contractor crossing borders, I was one before joining joining the Gummint and then traveled extensively with civilians who were both commercial and military from Boeing, Airbus, and other companies and still talk to a lot of these guys. No nightmares, just the routine nuisances of arranging for company travel logistics and reimbursement.
Other than the home country travel briefings and reporting requirements related to classified material,
they travel on their blue passports and have the SAME rules as any other civilian. Since COVID began the only Border change for the US employees is that they now have a letter on their company's letterhead to tell the Customs people they are on company business. With respect to quarantine and such, again, I keep hearing they have the SAME rules as for anybody else.
I won't speak to Canadian or EU employees because we have others here who are involved. This week a close friend who works in Iqaluit and has a wife in Quebec City was complaining to me about the time he loses to quarantine at both ends.