I think that would be possible, because dragonball super is a continuation of dragonball z.
Although dragonball super didnt continue from the end of dragonball z.
It continued from an earlier point, before the tournament that Uub was in and after the defeat of kid buu.
So the writers can basically choose if they will show Uub in super or not. They have created a situation where they have the flexibility to choose if they show Uub or not, without harming the dragonball super story.
As dragonball super is not a continuation of the end of dragonball z, but from an earlier point as explained.
It is not certain that Uub will be in super.
Besides didnt Goku say to Vegeta in dragonball z, that the earthling Uub could give them a challenge?
The writers hadnt thought of stuff like ssjgod and ssjblue and stuff like that back than.
Is Uub still a challenge to the dragonball super versions of Goku and Vegeta? Even if not going higher than their baseforms?
That tournament Uub isnt above kid buu right?
Maybe they dont count those tournament scenes with Uub as canon for dragonball super.
As dragonball super started from an earlier point in time of dragonball z. Before that tournament with Uub.
Which still allows them to show Uub in super btw, but they might change those scènes a bit or explain how Uub can still give them a challenge.