No, the Vikings had been raiding, what is now England and scotland, since around 700 ad.
Ragnall (Ragnar in the series) just did it better, from further away, and actually attempted to control the areas, instead of raiding and leaving. The vikings started hitting France from the Coast around 800 ad or so.
He did it better without following the coast the whole way, which was what they typically did. They most definitely knew it was there, they just picked a better route which saved time. (And what he is created with)
Personally I can't wait for Lagertha to break out on her own, because historically, she is a pimp.
Not to mention Ragnalls sons are fucking badasses, and when Ragnall is executed, they lay waste to pretty much everything they come across in England.
Danishnet.com has some amazing articles about all of the historical figures.
EDIT: I skipped past your point about the Jarl haraldsson, and you are absolutely correct. Personally I hated how they portrayed his willingness to kill the Blacksmith. That shit would have NEVER happened. Smiths were a protected class for the most part because their skill was so heavily relied upon.