I would expect that they are in one sense, a law unto-themselves.
Typically they would only take to the field of battle when their charge is present, their charge being the slann, so even if a scar-vet or even an oldblood was present, they would be commanded by the slann as he is the head of the CoC.
When not in the presence of the slann mage they are there by the slann's orders, ergo they will be under comand of the general, be it a scar vet or otherwise, although those orders will never superceed that of the Slann's.
Therefore, the temple guard, do not fall into the mainstream command structure, they are solely commanded by the Slann, who in turn may on occasion grant their assistance to the force of a scar-vet.
So to answer your question, the answer is yes the scar-vet does come above the RG, but only when the Slann provides that that be the case, otherwise the SV has no power over them...
Therefore your question, although thought provoking, is much broader than you have allowed for.
Oh and on the topic of Chakax, he is the last of his spawning, and given the reverence given to age by the LM culture he is held in high regard, although he is not a commander in his own right, to consider this point is to go down the path of discussing LM spawning, genetic engineering and breeding etc
-Eagle
