I mean… per UI Add-On Development Policy
Add-ons must be free of charge.
All add-ons must be distributed free of charge. Developers may not create “premium” versions of add-ons with additional for-pay features, charge money to download an add-on, charge for services related to the add-on, or otherwise require some form of monetary compensation to download or access an add-on.Add-on code must be completely visible.
The programming code of an add-on must in no way be hidden or obfuscated, and must be freely accessible to and viewable by the general public.
Notably these points, I think are where Overwolf might be in for some trouble; I haven’t personally used their client but if you are indeed forced to watch an ad or download their client in order to access the addon vs a easily reachable website it might not be deemed “publicly available”.
I would wager watching an ad is the equivalent of monetary compensation when it’s used as a hard download-gate without a skip.