To clear it up:
Pokeymans was developed by APE Inc under the name Gamefreak, their new name.
Thus, the copyrights to anything made under the name APE Inc do not transfer over to Gamefreak.
Ergo, since APE is responsible almost solely for MOTHER/MOTHER2's creation (so far EVERYTHING shown from the MOTHER series that has been in MOTHER/MOTHER2 has been in MOTHER3 as well and has gained all the copyrights), an Earthbound character will be in Brawl. Who better than Ness?
If you want to use the "well maybe it's items or blahblah" argument you are so wrong.
A better argument would be to use Onett, but stages and items don't get title screen copyright representation anyway. For some more clarifying Oxyclean power, shoot APE Inc in the Melee credits. The only thing to pop up on its card is "Earthbound".
Also; Third party crediting works a bit differently than second party crediting.