I can imagine an indigenous woman having a fling with a viking and just rasing the kid in her village. No one the wiser.
It would be impossible to know if this happened. Even if you found someone with both indigenous and Viking genetics, you don't know if it's because his great grandfather came from Norway in the 1920s.
The history of early American immigration is absolutely fascinating, there was a story of a Chinese man who just told everyone he was an indigenous American in order to avoid discrimination. I've actually met people from Eastern Europe who ended up working at Telemundo, no one can tell that they're not ethnically Hispanic. In fact, who to say what Hispanic is. There are plenty of Asians in Latin America, if some decide to migrate to America are they not still Hispanic ?