This is straight from the horse's mouth, AdSense Publisher Support.

A note on traffic exchange programs
We understand that our publishers are always looking for ways to attract interested users to their sites. But using third-party tools or services to increase your site traffic may lead to invalid clicks or impressions and result in your account being disabled.

Still want to use traffic exchange or link exchange programs? I think the last four words might have changed your mind.

Here's a link to the full article on AdSense's official blog.