Based on what I’ve seen in the forums, sentinel with void knight’s mastery echo for melee and void skills should be a full duplicate of the skill like you used the skill directly, including all triggers.
If you have healing hands with Seraph Blade (making it melee) and Cleric Hammer (making melee hits cast healing hands), the non echo versions will correctly hit and cast the spell version, but the echo version will only do the melee hit and not cast the spell version.
Expectation would be that the echo also casts healing hands on hit and all the associated effects happen as well.