You can mix UniFi and third party networking devices, but a full UniFi topology managed by the UniFi Network Controller gets you centralised network management with all of the advanced UniFi features.

A common topology including a UniFi Security Gateway, Switch, Access Point and Cloud Key 

A UniFi Dream Machine Pro system, with both UniFi Network and UniFi Protect controllers, providing power to your cameras and access points via PoE