Is adsense allowed to use on a nulled script collection blog? i had seen some nulled script blogs having adsense ads.. :-/
Nopes, I don't think that it is allowed since Google needs original content on the website (don't know whether ths comes in that category or not)
Chances are your account will eventually be disabled for being a risk to advertisers once you start making any sort of worthwhile money. People who would visit a site looking for "nulled scripts" aren't generally (not that there aren't exceptions) the type who like to pay for things, which defeats the purpose of advertising to them. Advertisers will cry foul and as it always does, click fraud will come out of the woodwork somehow, Google will have to let you go. This isn't to say you can't do it though. Like you said, you see other people doing it. Just don't let it come as a surprise if you get left in the lurch and have to forget about getting a last check.
Its against the rules and doing it is very risky. I would advise try some other type of advertising network with that sort of content.
No second thought: if it's illegal or on the borderline in any way in the us, it's probably against adsense's TOS.