If that's the standard you using, then no the Green Party are certainly not corrupt nor for that matter are either of the two big parties despite everything. (Btw as an aside, know how the CIA basically rigged the post-war Italian elections in order to make the Christian Democrats win over the communists? Despite being maintained for years this is now
not a conspiracy theory)
In general though Joe is Right. Also I suspect due to the nature of many Green Party activists that there is less corruption among the party's rank and file than than the "big two" but I suspect that is true for nearly all third parties.