The burden of proof on this subject is incredibly low. Corporate espionage has been around for a long time, this is far less damaging/shocking/expensive than that.

I'd say it's almost a forgone conclusion that it's happening.

Edit: From 2015

https://curiousmatic.com/professional-trolls/

Link in the article to Monsanto trolling:

https://naturalsociety.com/monsanto-and-others-caught-paying...