@ Dren: You are right. This kind of folklore is really interesting.
The totally opposing views in the two articles you listed also showcase how different approaches can be.
I have to say, though... the second article, while pretty interesting, has rather glaring weaknesses:
1. While it may be true that there are some obvious similarities between the Norse Odin and St. Nicholas (=Santa), the very fact of an existing resemblance between one bit of folklore from one place and another bit from another doesn't that there is an actual relation between the two. Just as two animals might use the same 'tricks' to solve some evolutionary puzzle separately, and so might be assumed to be close in terms of evolutionary kinship, while, if fact, they are not, the same can be true with culture. The author doesn't show how Odin might have emigrated to the low countries. There is no proof that there was much cultural 'contamination' there in the time that the Sint Nicholas folklore seems to have been born (by that time, the old Norse regions had been Christianized for centuries). Maybe there was a sort of cultural symbiosis, but it is hard to tell.
It is rather typical of art-historians and such to feel that it is enough to simply point to some cultural similarity and to assume that this proves an actual significant relationship between the two things. But to a slightly more serious historian, it isn't. (Yes, I am a snob about that sort of thing.
2. The story about how St. Nicholas was turned into Santa in the USA seems to be very inaccurate. Sure, in a way, Santa was reinvented by Coca Cola in the 1930s. But the sledge, the reindeer, the elves, etc. had already been written about before that in connection to Claus a long time before that. And there was a UK version of Claus as well. So it is unlikely that Coca Cola invented these elements out of the blue. Santa clearly had evolved away from Sint Nicholas into something resembling the modern version much more closely already. And when even the English wiki-page mentions sources for that, the author of that article probably didn't do her research.
And the other article...? Well, it seems to be a more coherent argument. It appeared to make sense to me (I remembered the first painting used as illustration, for example). Clearly, there are obvious resemblances between these 'black pages/slaves' (which you see in quite a few paintings from the 17th, 18th and 19th century, though they are usually not children). Are these always children? I don't think so. The 'Piet' from that dutch book by Jan Schenkman was clearly an adult. That part of the argument seems to have been included mostly to shock the readers.
The 'crux' of the argument would seem to revolve around this 19th century dutch writer Jan Schenkman. Was his book really the only thing that introduced the servant of 'Sinterklaas', the 'Black Piet'? If he did invent that part without any reference to existing folklore, then it seems that it is pretty clear that this 'Piet' was supposed to be of african descent, and that he was unrelated to the black devils of Austria, the ash-faced chimney-sweeps from other places or Odin's black-painted warriors. The outfits of the 'Piet' did resemble that of these 'black pages'. But was the author really directly inspired by those paintings? The outfit also resembles that of 'clowns' in general. Of the 'Harlequin' figure, somewhat, as well. The theory is likely, but far from certain.
Still, it does seem an odd coincidence that this Jan Schenkman would 'invent' a black servant for the dutch Santa, while elsewhere in Europe, we find traditions that also ascribe black (but not african-black) servants to Saint Nicholas.
Settle the question and win the Gorums Santa Claus Nobel prize for historical research!