I'm fascinated by the dramatic dimensions of this particular chapter of obscure history. Anything about the aspirations of the semi-mythic figures involved in this invasion (Sveneld / Oleg are the two I know about), or about the demographic elements of the occupation, or about the probably narrative of the invasion on both sides, is welcome.
They could well have been both; vĂkingr was a job description, not an ethnicity. Rus', on the other hand, is an ethnicity.
As far as what their victims would have identified them as, chances are they'd have been referred to as raiders, or the local term for it. The only Sveneld I'm familiar with, though, is a Varangian warlord who was in service to the Rus' of Kiev. Also, if you're talking Oleg of Novgorod, he was also a Varangian who wound up ruling a significant portion of the Rus'. As far as where they originated, though, that's not known.