"These jobs do not provide the same pay and benefits as military personnel but also do not come with all downsides of military service - they are civilian jobs and hence have a union. Sounds familiar so far but, unlike our contractorized servicing, it seems that these jobs also include a reservist commitment of so many days per year plus some deployments (voluntary?)."
Yes, a pre-requisite to be granted the job is that the applicant must join the Reserves (or already be a member) within a certain number of days from being granted the job, or be fired.
Actually, the pay for that civilian job (plus the medical insurance, etc) total well above the combined pay/benefits package of the active-duty personnel who do the same job.
I know this because a few years after I left the USMC I applied for such a position (I didn't get it).
Many civilian positions within the Defense field require uniforms... when a civilian tech-rep (technical representative of either a defense contractor or the DOD) deploys aboard ship with the USN/USMC, they are required to wear the khaki uniform of Chief Petty Officers... without rank or collar insignia. They simply have a name-tag that lists both their name and the name of the company or agency they are employed by.
I saw these uniforms when my squadron deployed on CV-61 Ranger in 1985-87 (I worked with 2 such tech-reps daily).