I've been hearing that sweepstakes are best on PPV, is that true?
Can they be made to work on display network such as Decisive?
Sweepstakes involve enticing someone with the offer of winning something valuable.
The desire people have for free things (and any benefits that object has) is universal. You can therefore run sweepstake successfully on any traffic source that serves humans. It all depends on the offer, the angle, the demographics, so basically everything that influences every campaign you ever make.
There are of course some sanity checks to consider, e.g. if Google Search are the keywords you're bidding on too competitive to make it worthwhile - and search traffic may just be too expensive in general.
But can you make sweepstakes as a vertical 'work' on virtually any traffic source? Yes.
^^ What he said.
Also something to note is if you focus on hearsay then you will always be behind the affiliate herd, which typically leaves slim margins and constant barrage of direct competition.
What Green says.
It would cost you 200$ to test it out for yourself 
The appeal of pops is that you don't have to worry about banners and the creative restrictions are very lax. Doesn't necessarily make it better imo.