The plaintiffs allege that IGE employees actually do the gold farming.

They may be defining "employee" fairly loosely, but that's the kind of thing that isn't going to come up until the late stages of the case, so is unlikely to undermine their claims even if the people who farm aren't given paychecks directly by IGE. And legally, if IGE is paying people money for gold (which they are) there's a reasonable argument that they're employing them, even if it isn't a traditional employment relationship.