Scandinavians were never part of a unified group and likely never called themselves Vikings. The term Viking referred to all Scandinavians who took part of overseas expeditions. They were not a unified political and cultural group capable of betraying one another. Between 790-1066 AD, Scandinavians were part of many small chieftain-led tribes that often fought each other. If they weren’t home fighting for the glory of Valhalla they were either raiding the coasts or settling foreign lands by adopting the local culture.
The only loyalty they might have would be towards their regional Juntas and families rather than a none existing Viking people. Those that became Normans were seeking a better life for themselves and families. Many of them being young men seeking adventure. They were tired of living in the frozen north where food was scarce. Many of the first Vikings to take up residence in Normandy were paid by the king of France to protect the coast from their own raiding brethren in exchange for good fertile land. Which they then used as a launching point to raid other coastal areas.