Didnt read entire thread so not sure what has been said.
At any rate, at first when I saw Vulpera could be warlocks, it felt rather odd. Then I thought about it. There is even a quest where Vulpera use dark troll magic to collect souls and use them to defeat undead troll along with player's help. I think it was made pretty clear that at least the vulpera involved knew very well how to use such dark items.
You could say that doesnt make them warlocks and I agree, but what it proves is that Vulpera dont really mind, if it gives them advantage. They have been shown to be survivors that use every tool available to survive in the desert. Darker magic is probably acceptable tool.
Hence... warlocks.