Ron, welcome. The center channel information is "maintained" just as discretely when it's played by the mains; speakers always have to play a multitude of different sounds and the center info is just another category.

Your proposed arrangement would have one of the two benefits that a separate center speaker can have: the ability to adjust the level of the center channel independently of the mains, to try to make low-level dialog more understandable. The second benefit, anchoring dialog to the center of screen, wouldn't be realized; the center image would shift to the side along with the position of the listener, but not farther out than the center channel speaker on that side. This is the same result that occurs when the mains are playing the center channel.

It's almost, but not quite, as philosophically painful to me as placing the surround speakers on top of the mains. But hey, it's your setup, and I could be wrong. Hope it works for you.

Anchoring the dialog to the screen was the initial reason why I thought of doing this. Puts the M2's right at the center on my tv on each side.

That'll handle vertically centering the dialog, but if you sit at all left or right off center from the TV, the dialog will appear to move in that direction horizontally.