Goku Black has been a topic of discussion ever since the game was announced.
Originally, the discussion made sense because we didn't know if they were going to include Super as part of the game's story/character roster. But now that we know beyond a shadow of a doubt that Super is gonna be in, OF COURSE Black is gonna be in. Only question is base roster or DLC.
But despite this, people keep saying that technically Super isn't being considered, that all the stuff can still be traced back to Z and stuff to which people hype up Black and post that gif and that Zamatsu gif and that Goku and Zamatsu hugging gif I think I've seen it a million times why do people keep posting that gif we get it he's cool.
Do we know this for a fact? No public build with with SSB Goku/Vegeta exists yet.
I mean it's technically still POSSIBLE that this might be the case. But considering that's not how Arc Sys typically handles characters + the fact that they're unlockable separately from playing the story mode and stuff + the fact that they got a separate reveal and gameplay trailer leads me to think that they're their own characters.
Plus with how animations work for GG Xrd I doubt they're gonna put in that much effort for characters that ultimately amount to "different versions" of the same character, they're probably gonna want them to be full fledged characters and treated as such.