The Dukes of Pomerania, started marrying into mostly German families from about 1250, so well before Erich/Erik.
I think based on their close ties to Germany, as members of the Holy Roman Empire, and eventually a part of the Kingdom of Prussia, I would go with German names at least during this period. The Euroaristo naming policy is to use the dynasty name, though there are many profiles that use the geographic names.
Incidentally in Europaische Stammtafeln, book 3 it has Erich with the name Bogislaw in brackets, perhaps he was originally called B and then changed his name once he inherited or became heir to the Scandinavian thrones?