Hello mate,
We have shared document and library to any developer and provider can deploy a their own service as current our service.
So, you can update extensions from their service.
Unfortunately, we dont have a tool to check that how many provider used our technology.
This guy is maybe an one of them 🙂
http://www.joomlart.com/forums/topic/how-to-use-extension-manager-with-online-repositories/
If you like our service, please help us to share this guide to more developer can know about that
http://wiki.joomlart.com/wiki/JA_Extensions_Manager/Developer_Guides
PS: you can use local service to update other extensions that not of JoomlArt.
Best regards,
ThanhNV