A1. By @ImTheGroom :
They do work just fine. I was at dinner with a fellow in just that combination a couple of weeks ago, and he looked very sharp. I'm personally a fan of Marcella and flat front shirts, in general, but if you like pleats, there is nothing wrong with them at all.
A2. By @MrDaniels :
I am not that worried about "rules" but I think a flat-front shirt looks better with a three-piece tux.
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