This kind of system may only safe for beginners. But later on, google will notice you if you are using traffic exchange program or not. In short, no safe traffic exchange program for now.
No, traffic from traffic exchange site is not allowed. And those traffic never generate income so, forget about those low quality traffic, try to focus on targeted traffic
NO NO NO NO, only legal traffic is allowed (no work around solutions), don't get smart with the system, unless you know how to be !
It is against Adsense TOS and never do that. Your account will get banned after few days even if you try to be smarter.
You can use athits.com they give no referrer traffic adsense safe, for more security you can upgrade and choose your own referrer
Traffic exchange sites are strictly prohibited by adsense as a traffic source. Better don't use it. TE's are just provide junk traffic only.