I'm running adsense on my site. Can I run adsense on a subdomain of the same site without asking google? Secondly, will google consider the subdomain as a separate site or the same site? If the traffic conversion of the subdomain is poor, will my main site suffer?
You can run adsense on a subdomain without asking google. In terms of search engine rankings, google considers subdomains as seperate sites.
I suggest that you create a specific channel for every Google adsense code that you add to your subdomain.
You can put AdSense on any of subdomains (even on free blogs like blogspot) and on any other domain without Google preapproval. Google will find out where AdSense blocks are and there is no need to announce about it? The most important is not to do anything against Google TOS and I would advise you not to put AdSense on subdomain if on the main domain is something that can be considered as against Google AdSense TOS and rules in general. (adult, gambling etc)
you can put every page in the world in every site - but the site must not break the tos of google. a lot of free hosting companies give you free host and put their adsense
I think google will mix all your sites together, so if you do something against TOS on only one of your sites, you might lose your whole account for all of your sites, so as long as you follow tos you should be ok