I like to think of them as Native Americans. Use all parts of anything killed as not to waste.
Considering all the wars they are in, thats a lot of human/gobbo/dwarf materials.
What I wonder is, since it's the elves themselves that do most of the dying, what do elves do with their own dead? It's a sin to let anything go to waste right?
Elves don't use products that are made from animals even if that would be a waste. So I don't think that is a factor here. Including that it is HIGHLY doubtful that Elves eat their enemies whole.
Besides the Native Americans had no problem mass killing animals as it was and not only crafted metal objects but had no stigma over buying, selling, or making animal products. Also their government is drastically different to that of the elves (Elves in Threetoe seemed to be some sort of odd Monarchy mixed with a Council that anyone and everyone could just barge in and get voting power with god veto power)
Oddly despite it being called "Elven Retreat" the elves don't seem to treat it as such. Meaning that they don't have "Summer" or "Winter" homes like many of the Native Americans did as well.
I think the comparison of Elves to Native Americans is a bit premature... They are almost nothing alike.
Of course I probably just don't see that the comparison is just being done for fun and your reinvisioning the elves in that respect.