IMO, whether or not the glue fails first and the joints separate, or the glue holds and the boards crack, is a matter of the T&G design. If the T&G were made like or similar to the standard NOFMA profile (which is for nailing), then I think the boards could separate as the glue surface is not really very much.
Also, notice that the instructions for gluing are for the end butts. This is to keep the joints closed. The clips are too flexible And full glue up is only on the shortest of boards because the clip placement isn't adequate for shorts. I'm not sure WHY you're letting the installer off the hook. What is his excuse for failing to follow the manufacturer's installation instructions? All this is really his problem, not yours. At this point, I'm guessing you do not want to go through the hassle of having the floor removed and repaired or replaced. I understand. Perhaps calling the technical dept. of the manufacturer will get you the answers you're looking for.