By default the HideSCAHealth string value is not in the registry. It's only added with a data value of 1 when Action Center is disabled. Deleting HideSCAHealth, or changing it data value to 0 (zero) would normally enable Action Center again. The REG files and group policy do the same thing for this registry setting.
Since the find and find next didn't find any HideSCAHealth entries in your registry, I'm thinking that there's got to me some other unknown item affecting this than the normal group policy setting for this. Unfortunately, I'm not sure what else it may be yet.