Being on official f-droid categorically means no proprietary sdks. The app could still make calls to random servers, but that would be in the open since the app needs to be open source.
F-droid doesn't have non-free software. F-droid flags some apps with anti-features for various reasons like non-free network services (https://f-droid.org/wiki/page/Category:Apps_with_NonFreeNet_...), which is quite useless honestly since it makes no difference even if a remote service is free since you don't control that end. Perhaps historically f-droid allowed non-free dependencies (https://f-droid.org/wiki/page/AntiFeatures), but I don't think that's a thing any more. I don't see any major apps in that category.
