Wheel weights themselves are not a bad idea, nor do they unbalance the wheels.
Home made Cement wheel weights will be nearly impossible to center, balance and keep straight. What ever the weight 200 / 400 pounds? not in balance bolted to the wheels or axle in not good for the the tractor. 1/8" Steel plate is far to thin and will soon bend or rip out.
Big difference between Static weight (ballast box) and a rotating weight.
Loaded or filled tires is another whole story and he didn't ask about that.
I don't know if it matters all that much when you are traveling 1-6mph on a rough dirt surface. I understand the need for a balanced tire on a vehicle traveling 60mph, but I just don't think it would be an issue with a tractor. I do agree that the 1/8 steel plate would be too thin.