DBZ is a point of SERIOUS contention among character creators, forums, so on and so forth. Especially with how powerful the characters are, what with the second big bad being a planet buster class. The Namekians, Saiyans, and Changeling's abilities to change forms ever so frequently. Allowing them into this scenario would lead to so many arguments about power level that it would be comically unwise. 

But again, I plead for people to not saturate this roleplay with Fan Characters.