No, you have to put the adsense Ad codes into your website. If you dont do this Ad will not be published on your site and you won't earn a single penny/
I guess this is will not work either since adsense provide individual publisher id to their advertiser so there may some kind of codes included in the advertise code. Not sure though.
Well you can but only that persons code should be in the site. If your code is there too then you have to remove your code. you can't put 2 codes in same site.