All Kaltura clients are licensed under AGPLv3 and all PHP clients support both PHP 7 and 8.
They can, and are in fact, used by all of Kaltura’s official web interfaces (Admin Console, KMC, KMS, etc) so yes, you may utilise them in any third party project to interact with the Kaltura API endpoint of any Kaltura ENV (SaaS, CE and OnPrem).