I just deleted a text in Message+ on my Droid Turbo 2 and when logged into Message+ on my PC at the same time, it synchronized and the message was immediately deleted. The reverse as well, on my PC in Message+, I deleted a message and immediately on my Droid Turbo 2 the message was deleted. It appears the synchronization of Message+ and devices does handle the deletes.
...Just another VZW customer...trying to offer some assistance...