Aren't all Pokemon technically nude? So shouldn't it be added as a tag to all Pokemon pics unless clothes are obviously present?

Pokemon are also generally considered feral, and ferals aren't tagged nude.

If there is a human trainer in the pic and they are nude then its relevant. If its a Pokemon that has been "humanized" or is "anthro" it could be applicable as well.

Nude tag generally applies to if the character could be wearing clothing, as obviously clothing would not exactly fit a feral character. While an anthro furry does not need to wear clothing, in the absence of any clothing a nude tag could still be relevant.

I'd agree with Vixxxine69.