For the uninitiated, what would it mean if Russ was allowed to intervene?
Nothing. The outcome would have been the same. Hence, there was no real point granting it or even looking at the petition closely.
He would become a party to the case. Specifically, he wanted to become a party as a defendant in that case.
Had the plaintiff actually named him as a defendant, he would have likely been dismissed from the case sua sponte as clearly not an actual defendant, having no connection to the case whatsoever. Generally, intervention as a party defendant would only be available to someone who could validly have been named a defendant by the plaintiff in the first place.
Greer is not a real party in interest (usually a term applied to plaintiffs but Greer tried to do it in this weird backwards way). Had he been joined as a defendant and somehow the plaintiffs won, he would have been subject to the relief the plaintiffs were demanding, which would have been nonsensical.
For instance, he would have been enjoined from enforcing the Nevada statute regarding brothels, something he can't do anyway because he isn't Nevada. He would have had to disgorge his profits from prostitution, which he doesn't have. On the other hand, he would also owe the plaintiffs' attorney fees and costs as a prevailing party, presumably on a pro rata basis with the other defendant(s). Or maybe joint and several. Who knows (or cares)?
So at the very worst, he'd end up not able to enforce a statute he already can't and owe a lot of money.