I've seen tiny two-man trading desks pull in a million dollars a month from a single customer, so I hope you're not suggesting that the volume of money means that they're actually providing a million dollars of value to the advertiser.
What you're describing sounds like many affiliate and CPA programmes, except for the part where they're paid on new sales on users returning for thirty days.
If that's true, then it sounds like the advertiser is actually receiving value, and yes: someone who knows how to use advertising to actually generate new sales absolutely does know what they're doing.
I don't know why they'd keep it a secret that they're successful: Every brand in the world would want to hire them. The biggest agencies in the world would 10x their income immediately just to get them to come in the door.
I mean, who wants one million when you can have ten for less effort?
The thing is though, I've never seen that, and you're not coming out and saying it. I don't know if that's even what you actually saw, and as you can see, it doesn't "make sense".
It's my experience, these "paid signup" companies fall into two categories: One where three-to-six months later they turn out to be chargebacked stolen credit cards, or it's actually drug money that's being washed.
You can live like a dude on that kind of money, but it doesn't mean that the advertiser is actually receiving that value.
I'd absolutely want to hear about this.