By Flat Grind, do you mean the blade itself flat Ground to 3/4 or full height, or a flat grind bevel?
If you mean a bevel, no worries about the lamination lines, you may eventually sharpen back to the lams, but they just grind back with the other steel.
If you mean flat grind on the entire blade, this will likely change the appearance of the laminations (I'm thinking making them deeper, or further back from the edge) and the blade would thin out a bit. But I don't think it would affect the overall performance of the knife.
And no, I have never seen one, or heard of anyone, doing a full height flat grind.
Kevin