As far as I know, this is correct (from studying early English naval history, that is). "Mixed nationality" crews were common because men tended to follow a leader and could change allegiance over time, so a man's origin would not necessarily determine his allegiance to a leader.

Also, keep in mind that "Viking" is a modern term that covers a wide variety of peoples, while at the time in the Norse tradition "viking" was a verb -- a thing you did, not a way to describe yourself. A Norseman might "go viking" for a period of the year and then go back to his farm.

Unrelated to your question, but: The types of ships used for mobile warfare were broadly similar across northern European cultures, and were copied by the kingdoms in what would later become England (Alfred the Great in particular built a small fleet of longships to the Norse model).

Yes actually during the migrational period boatloads (pun intended) of immigrating jutes, saxons, angles, Frisians and even Norwegians were heading towards england.