It is true, but not only for vikings. Take for example the French settlers in North America, who assimilated native Americans culture and technology. Comming back to vikings, such an example could be seen when they settled in Normandy. Progressively, they took many French/western European cultural traits: Conversion to christianity, French language (and creating their own dialect), ways of ruling, etc.

That simply comes from the fact that vikings, when settling somewhere, are becoming a minority towards the surrounding population, thus increasing the amount of cultural influence they get from outside. It also can be explained by the fact that if you want good relations with the people where you settle and basically mix with them and not be separated, you need to show them you are open to them. That is one of the reasons of the acceptation and conversion of vikings from Scandinavian paganism to Christianity

I suggest digging into works of experts in the matter, such as Anders Winroth or Regis Boyer (if his books are available in English, I have never searched)