92 of top 500 subreddits are moderated by 5 accounts.
That's not the way it works. You can steer things your way for a while but everyone is looking for the conspiracy. I knew a guy who was dumping affiliate links everywhere (because everyone was innocent once) and flagrant shit like that was making him a couple hundred bucks a day. But you're discounting the deep distrust all the ad agencies and content producers have for Reddit because they lie about their metrics and consider themselves unaccountable to everyone. We ran $10k worth of advertising on Reddit once because we were true believers. And despite the fact that I had a herd of anime lovers running ads about new anime for anime lovers in /r/anime, the end result was a bunch of doxing and flamewars and DDOS of servers because, and I say this with no quaver in my voice, The Reddit demographic is utterly fucking worthless.
100% chance it happens. Those scandals happen all the time. The thing is, the money being spent is modest because the effect is modest. You're generally talking about mid-level Facebook advertisers with like $5k buys, $10k buys. If you're at all good at computer it's a shitty way to make a living because moderating on Reddit is fucking awful. You're doing it because of the somatic fame/power/dickhead hit not because of any financial influence.