The BP functional test actors are triggered because the BP Functional Test manager is triggered by the Engine automation test framework. And this framework knows about it because the BP functional test actors have a post edit callback that store information about the tests into the Asset registry.
So if you are going to instantiate new BP functional test actor on a client build the test framework will not know about it.
The BP Functional Test manager will not be triggered.
The BP functional Test manager make it easier to run what is available in the loaded map. But if you have other mean to trigger your tests it is all good.