UI omen Goku should win this.
If Vegeta's fission ability would work on KI in general, then he probably would beat UI omen Goku - but it isn't...sooo
Yeah, it's a very interesting ability. To think that he can do way better than someone who is stronger than himself (UI Omen Goku) with this technique against Moro, and not only against Moro, he could do the same to Zamasu, Kefla, Buu and even Vegitto / Gogeta etc. if he knew it back then.
I think it's necessary for Goku to learn this technique as well, he can't stay desperate against the fused opponents.
But since it doesn't work on non-fused opponents, UI Omen Goku should inflict enough damage to SSBE Vegeta until his UI time limit is done, if Goku is faster than Moro, and if Moro is even stronger than SSBE Vegeta when he doesn't lose his absorbed energies, then Vegeta will get blitzed by UI Omen Goku, SSBE Vegeta's only chance is somehow resisting to UI Omen Goku's extra super fast blows with moderate injuries until Goku's UI time is up, and that's not impossible if Vegeta knows about UI's time limit (and he knows) and if he only fights defensively in this fight, he might have a small chance here. But in normal circumstances, the power difference is too big between UI Omen and SSBE, especially the speed difference.