Not according to what I'm reading. From the author's own source:
these birds feed on Raphia and Elaeis palm fruit but will also take invertebrates, fish and carrion. When feeding on palm fruit they hang upside down below the fruit, pull it off the tree with their beaks and then hold it in their feet to eat it. Interestingly they have started to use a similar technique for taking carrion at game lodges. At Samburu Lodge the staff bait a branch to attract Leopard, they hang a goat haunch below an angled branch and the Leopards lie along the branch and haul the haunch up to feed on. The Palm-nut Vultures have developed the habit of hanging below the branch, using their palm fruit technique to enable them to pull off strips of meat.From here:"Sometimes also small birds and mammals, lizards, crabs, molluscs and locusts (grasshoppers), frogs and carrion."
And another source: "Unlike other vultures, the palm nut vulture often catches live prey---both on land and from the water. On several occasions I have seen them grabbing fish with their feet from the lake surface and then carrying the fish to a tree or to the lake shore to feed on it."
That's an awful lot of flesh for an "almost completely vegetarian" species.
Both of the sources you listed make it clear that the diet of these “birds of prey” is almost completely vegetarian.