ReadyNas with user groups from MySQL

Hello,

I am probably going to purchase a ReadyNas capable of handling up to 16TB.
ReadyNas has it's own ACL user group system for folder permissions but I was thinking if its possible to use my own way to create user groups using MySQL and PHP addons for folder permissions is that possible?

Lets say, a visitor uses/login to the front-end website through LAN to signup for an account to use ReadyNas space on server. Now he may use the server for streaming videos/images/music and also upload to his own available folder space.
So a ReadyNas will need to load the database from MySQL for permission on folders according to user groups created by the admin. If it's possible to have a custom MySQL database for ACL on folders permissions then can the user access the server IP location (LAn) for let say access PLEX addon for streaming videos but again according to user group?

I am sorry but couldn't find a clear answer about this.

Thank you.