Yes, we do monitor Facebook comments!
In the monitored pages section of your alert settings, you can add any public Facebook Business page. You will then receive all the posts and the comments from the 100 latest posts published on that page.
Mentions from Facebook that match your keywords or query
If you want to get mentions from Facebook that match your keywords or query, you will only get the posts that have been published by public Business pages on Facebook, but not the comments. It is only possible to see the comments of those posts when opening the mention in the app.
Find more information here about how Mention monitors Facebook.