Was told by surgeon that pulling abdominal muscles very tight during TT would not affect Pelvic Floor Prolapse Issues, true?

Before a week ago, I would have told you that there is not much to worry about. But I just recently had a patient who had a recurrence of a surgically repaired pelvic floor prolapse after her abdominoplasty. This could have been a coincidence or it could be that the increased abdominal pressure from the rectus plication contributed to the recurrence. I think that you need to understand that there could indeed be a relationship between the tummy tuck and the pelvic floor stability and that it will be an additional risk to your procedure. The risk of having pelvic floor problems is still likely quite low, but not zero. Avoiding excessive tightening of the abdominal wall might be a good decision.

Its often helpful to have another consultation opinion, even just to confirm your first impression.  The main issue with pelvic prolapse is a loss of support of the pelvic structures, and any increased abdominal pressure will be secondary, and is unlikely to affect the prolapse. I am not aware of any link between plicating the abdominal muscles during abominoplasty and worsening prolapse.  

You are correct to consider another consultation.  A tummy tuck with tight muscle imbrication will increase intra-abdomenal pressure and could aggravate pelvic floor prolapse, even raise your diaphragm position.  Best to seek a uro-gynecology specialist to work with your plastic surgeon on staging your strategy.