Is paying for visitors to my site against AdSense policy?

Well, the key thing you need to ask yourself is whether you’re paying for people to visit your site, which is the purpose of all advertising, or whether you’re offering to pay people to click on the AdSense ads – or any other ads – on your site? If it’s the former, you’re fine because that other site then basically competes with things like Google’s AdWords program and every other advertising network online. No worries.
If it’s the latter, however, well then you have an issue.
The key question to ask is whether what you’re doing would be a service to the advertisers who use AdSense to have ads show up on your site or not. By the same example, let’s say I have a friend come onto this site and say “hey, let’s make Dave some money” and they proceed to click on ads left and right.
Is that good for the advertiser? Of course not, because as soon as they get to the destination page that’s the advertiser’s Web site, they’ll just bounce back without ever being a potential customer. And that means that the money that the company pays Google and the percentage that Google then pays me is all wasted and ultimately fraudulent.
Not good at all, and in matters of advertising, if it isn’t good for the advertiser, it’s likely not good for the publisher either.
On the AdSense terms and conditions page, it also says this:

Long and short of it is if this network you’re considering is going to involve a program that encourages people to click on the adverts on your page in any manner, then you’re right to avoid it and be leery. Because the alternative is for you to have your account shut down and any unpaid balance vanish.
Really, the easy way to think about all this is simply to ask yourself “is this really going to help the advertiser sell more stuff?” If that’s not the case, it’s not going to be good for AdSense and, ultimately, not good for your account standing either.
It’s the Google mantra become personal: Do No Evil.