That's one scenario. However I think the word Marauder is being thrown around as a general term here, probably started by extras who weren't really told much about what they were fighting about or who they were and making general assumptions, and now everyone is running with it. That includes the one guy listed on IMDB (which is not always 100 percent accurate)
Also I seem to recall conversations here not long ago where people were very insistent that Thanos would not go to that much trouble to get his hands on Loki (we were considering the possibility of him showing up at the end as part of the after credits scene and grabbing Loki then). I do think it seems rather unlikely he'd send a large force to go collect Loki like this, I think Thanos figures he will get him when he gets him, or he may have other plans for him, or he may be too concerned with other plans to "court death" to bother. Plus this film will be about the 9 realms and Thanos and the Chitauri appear to be outside of that from what I can tell.
Spoiler!!! Click to Read!:
also I've seen referenced a notice from Shepperton studios when filming in Bourne, saying it would be about 300 extras and a "battle between two kingdoms ensuing before the God of Thunder himself, Thor arrives and saves the day.”
and that would again, point to "kingdoms" which I really dont think a random group of marauders hired by Thanos could possibly be considered a "kingdom". However Nornheim, Vanaheim, and even Niflheim could all certainly be considered kingdoms. And the fact that Thor has to come in with his Asgardian buddies to try to break up this fight between two kingdoms, would pretty clearly indicate that it is likely Nornheim vs Vanaheim or vs Niflheim and not Asgard vs anybody to start with (just to finish it). of course the studio notice might be misleading but I would tend to assume it's correct and take the clues from that.
also found on another site, it says someone got offered the part of a leader of a "marauder army" due to his ginger beard. now again, the word marauder being thrown around as a general term more than likely. and I would question why would he have to have a ginger beard, unless, he is meant to look like either Vanir or possibly Asgardian? Certainly wouldnt need that for a random marauder....