this has never been proven. but it was the final blow to his public image after the rape charges. from then on most intel / infosec people who still remained partial moved on to condemning him.
Even if he had collaborated would it matter? what it proves is that you can not do OSINT and be "independant/neutral". bellingcat and all other self-proclaimed citizen journalists know it too. the message here is "if you stand up against the US and hang out in a FVEY country you're dead".
collaborating with enemies of US (no matter if DPRK, Iran or whoever) would be justified considering the nature of the material which was exposed. but doing so without thinking about his location and safety is the most "I can fix society because I'm a hacker" thing I've ever seen. it is a small crime though in comparison to the shit the US has gotten away and still does so until today. e.g. Gitmo and black sites are still operating, drones still kill civilians, their war on terror will go unpunished, people are still being brainwashed into believing "US army good", the CIA is still executing people overseas the same way as the FSB, while they shout "terror" or talk a big game about "law and justice" their crimes can't be held accountable in the ICC: pot. kettle. black.