Well then here goes.. I can say for sure on what I know soft canon wise for varies reasons that Danny Phantom has a shared universe with nearly all the Nicktoons up till around the cartoons from 2011 .. While sold and firm canon wise Danny Phantom has a confirmed shared universe status with the following Fairy odd parents(and by extension do to crossover Specials that cartoon had with Jimmy Neutron; Boy genius).. T.U.F.F. Puppy and Bunsen is a Beast.. The sold and firm confirmed canon is do to this short
https://www.youtube.com/watch?v=B8I8vhGHC2E
So we have a lot we could toy with in varies ways if we so choice to in some manner without having to make some excuse for it...
Though I can't help but think of how Dani with Fairy Oddparents would be once Fairy World caught wind of her existence