I'm just wondering if it would be okay for me to create a tag like this, or if it's something that would be unfitting or too subjective.

The reason I'd enjoy such a tag is because a lot of the animations I have seen where the animation have consisted of characters drawn frame-by-frame have often been of a very enjoyable quality. Whilst many of the flashes using the more typical flash "symbols" or what you call them, often feel very rigid and bland.

This tag would not be separating "good from bad", because either side will of course have plenty of both no matter. What this tag would do would be to separate a certain kind of animation, from another kind of animation.

The name for the tag is also not final, should it be approved I would not mind if anyone would be able to come up with a more suitable term.

traditional_animation?

If that one could apply to things drawn frame-by-frame in art programs I would be fine with that

Use it, see how it goes.