I am planning to make a website or blog about flash games, and I am planning to get flash games from sites that distribute Flash Games for free. No my question is, is it safe to put Adsense to this site, even though I get resources from other web sites?
Yes it is safe to put adsense ads on your page. The only effect of copying stuff is that your position in a search will decrease. Im not 100% sure about this information but I beleive so.
assuming that the resource where you get the flash games from allows you to publish the games, then you're ok to place the code on your site. However, if you don't obtain permission, all that will ensue is a DMCA to your site, if you're in doubt, refer to the ToS for adsense