If green is poking out the top it will still grow, but not as fast if the ground is just moist. But if it is completely underwater, it will not grow and eventually die if water does not drop to where it is poking out the top, it needs oxygen and sun. Planting millet is a real crap shoot. I did it for 6 years on private, had 2 years it was really good, a few that were ok and a few not good at all.
I could let water out, but I could not pump it in, and letting water out really hurt me a few years because I never got the timely rain to fill it back up. If you can let water out, and pump back in, you will have better results. Otherwise, plant and pray.
You have to really enjoy messing with this, otherwise, you are better off just letting moss build up, because the birds feed on the bugs in the moss.