It should be possible, though I would
very strongly not recommend using the same email as you use for actual communication (if you have already set up a separate "bounce" GMail account for your forum then I apologise for the emphasis, I just wanted to prevent possible data loss should you get it working) - vBMail will delete all the email it has collected from the mail server in order to speed up future fetching.
Without seeing an error message (you can see any connection errors by manually running the collect bounced mail scheduled task) I can't help, unfortunately
Fillip