You're missing the point.
It's not that this guy was paid off and therefore changed his views.
It's that he published research that he claimed was independent that was not, and in the process neglected to disclose his sources of revenue and conflicts of interest.
Those very conflicts of interest would, under normal circumstances, force folks to question the nature of the research and the quality of the results. IMO that's getting awfully close to academic misconduct. It's certainly extremely unethical.
Edit:
BTW, "Merchants of Doubt" has covered this territory extensively, so to be honest, I'm not sure Greenpeace has added much to the dialog, here, aside from flat out catching folks in the act.