The only thing the TPWD says about millet is the you can't hunt over it if it has been manipulated the first year. It would fall under a flooded standing crop in the rules below. The second year it is considered natural vegetation. It also doesn't differentiate between Japanese Millet and all the other varieties of millet.
A hunter may hunt any migratory game bird:
�over standing crops, standing flooded crops and flooded harvested crops;
�at any time over natural vegetation that has been manipulated. Natural vegetation does not include planted millet. However, planted millet that grows on its own in subsequent years after the planting is considered natural vegetation;