One of the Nabble Team will be able to give the definitive response on their advertising suppliers. Certainly, Google's AdWords appear on some applications, but on others various type of banner will appear. Those ads may not be purchased from Google.
It's worth pointing out that Google Ads that appear on your computer are highly dependent on the sites *you* visit and the terms you use in Google searches.
It is highly likely that your visitors will see completely different ads to those you see when visiting your Nabble forum. Only if they also visit your competitor's sites or have searched widely using terms that also appear on your rival's sites are they also likely to see your competitors ads.
Volunteer Helper - but recommending that users move off the platform!
Once the admin for GregHelp now deleted.