I think of Dark Matter as more Neutral Evil; he does whatever he wants but has a standard, not that it's one that he tries to match with anyone else. As far as he cares, this ancient ruin is free game, first come first serve. But he's not so stupid to think that just because the giant robot is dead, that there aren't any more traps and protective measures down there. A partner would be nice, and Dark Matter isn't the type of person who'd betray you just for greed. Not so much because of honor (Though that's what he'll call it) because it's not professional. It's like a bounty hunter betraying a contract he took just because the bounty would pay more; those types of people are dishonorable and unethical businessmen.