For a layman I just really know my shit when it comes to these subjects, I'd want to as well as it was a big part of what I studied at school, though I'm by no measure an expert.
I was under a similar impression as
@Zerô that the viking identity had something to do with Woden and maybe a local rugby club (not a local so I don't know).
I could give you the history lesson if you want.
I always thought the Raiders referred to “raiding” Sydney of their NSWRL premierships. And that the LA Raiders (later Oakland, soon to be Las Vegas) were inspiration, similar to Denver Broncos and Dallas Cowboys.
Yeah that's half the story.
To give you the short version the Raiders developed out of the Queanbeyan Blues (to this day they effectively are just an extension of the Blues), initially they planned for the club to be called the Canberra Blues (which BTW would have killed support for the club in Canberra before it had even got off the ground), but for obvious reasons at the time the NSWRL wouldn't allow them to participate as part of the comp with the blues name and what was effectively a Cronulla jersey and colours, so they had to come up with a new brand for the NSWRL team, some marketing guy (or whoever) came up with the Raiders, cause they were going to raid Sydney of all their trophies as you say, and Les McIntyre and Don Furner Sr. (I assume) liked it so they went with it.
The viking thing just developed naturally from the logo looking like a "viking" and people (particularly commentators) referring to it as such, I don't think it was intended to be a viking when it was first designed and announced, and it definitely wasn't referred to as such (at least by the club) in the beginning, I remember for a little while right at the beginning of the club some of the fans (at least the ones I hung around with and knew) used to call him Asterix.