Think they supported him when Vietnam invaded, but any support during the civil war would have been dwarfed by the support given to the Khmer Republic. You could say that they opened the door for Pol Pot by weakening Vietnamese factions, but that isn’t really providing support in my opinion.

The reason that Pol Pot is a decent example is because he got a fair amount of support simply for being anti-US (from for example) . The US covertly supporting an anti-US faction to keep their bigger enemies (Vietnam) from becoming more influential doesn’t mean that they were perceived as an ally of the USA (once again, prior to Vietnam invading).