Sorry, no I am not quoting officially or unofficially over MariaDB, I do not work for Interworx but was soo impressed with IW, even though we hold full unbranded licences, we have not rebranded as it is an excellent selling point.
Interworx uses MariaDB with centos 7, but I do not currently use Centos 7, either in test servers or production, however, from time to time I will load a Centos 7 test server, time permitting.
Interworx use their own services, so upgrading MariaDB or Mysql should be fine, the versions you install or upgrade are up to you, but as I have not tried MariaDB v10/10.1, I could not honestly say if it would work, sorry.
I do know PHP 7 works, as I have tried this on test servers, but as there are currently no Ioncube loaders or Zend (granted Ioncube have a Beta out now), we do not use PHP 7, but it does work if you do not use ioncube or Zend.
Also, I just checked on 1 of our NS, and that is using Mysql community edition (5.5.5), so my thinking may be wrong, or it may have progressed since I last looked.
I do know a lot of users use Centos 7, so hopefully they will post their experiences
I hope that helps