My first point is that you can be a little creative in how you say who you are. "I'm a researcher trying to find out how users are working with the UniCorp product" will get you much better answers than "I work for UniCorp".
My second point is that online forums tend to be a very focused group of people - most of them will be there to either complain about a product or to find ways to do the things they think they should be able to but can't - Either way, it's a negative relationship from the start - This will skew your results.
You would be better off getting hold of a list of users (talk to your legal department first) and emailing some randomly selected people with either an invitation to a video call (which you can record for further study) or just the questions you'd like them to answer.
Forums are a great place to see where your product might be falling short but they're not the best place to get a balanced opinion.