I run one in a 5gal dwc and by the time I'm done there's not even enough room for the roots of even 2 plants. I personally wouldn't suggest going over 1 per bucket, I'd run two but you have to know that the roots will turn into 1 tangled mess and if you have a problem with 1 it's going to effect the other and just cause headaches.
As for the answer, yes it's absolutely okay to put 1 in each 5 gal with a 3 inch net pot.