We have a similar tradition in Bavaria where I origin from, there Saint Nikolaus, which is essentially Santa is accompanied by a scary Krampus who punishes the bad kids, (not really though) his face is smeared with ash to make him look scarier. So your 'Pietens' might not have been a hint on black people but just a scare thing or it's a combination of the three Kings that followed the star to bring baby jesus the presents. They were black.
So I don't think it's racism, I think it's stupid to try and change all traditions and fairy tales because our warped minds find some suspicious 'ism in it.
I would suggest to let actual coloured people play these parts that could lead to more acceptance, when kids learn that they are the same as white people.