If it is in a sense for justice, then yes it could be considered good. I say justice, sort of like putting the wrong doers in their place and making them look stupid. This is somewhat rare though. I'd go so far as saying to do "good trolling" were people who were against Scientlology, or making fun of Tom Green's show. There is also the trolling that proved the ineptitude that is Wikipedia. Basically a professor successfully trolled an article, with help from his students, in changing the article's validity based on rules set by wikipedia.
Of course there are too many examples for the bad trolling...