Wordpress - Update plugin from personal API

For the benefit of others who find this page, I suggest those wishing to provide their own updates outside the official WP repository check out this project on GitHub, that demonstrates the functionality:

https://github.com/jeremyclark13/automatic-theme-plugin-update

Yes, this is possible. There's an entire chapter in Professional WordPress Plugin Development dedicated to this. If you haven't already, pick up a copy. It will definitely help.