Yes, from what I understand they're basically the vestal virgins of the US Army. Their role is deeply ceremonial, intended to be a symbol of the ideal soldier so as to provide a worthy guard for their fellow symbols embodied by the unknowns. They even literally live right there by the tomb, and their name can be obliterated from the register if they fuck up too badly, even years after their particular tour with the "Old Guard" is done. Their weapons, particularly their pistols, are literally totemic ritual objects.

Sentinels in particular get picked because they are true believers in the mission, physically look the part, have the physical tools to endure the monotony and weather, and they are wired to be the type of guys who get off on following regulations to the letter. For all those reasons, they are typically pretty young, as well. I've read a few accounts that suggest they're often not super pleasant people to work with later in their careers, but they're earnest AF.

They're probably elite in a different way than special forces, but I'm sure their military skills are as good as they can manage with all the other requirements, and at any rate I doubt you'd want to cross the platonic ideal of a Dwight Schrute while on his turf.