I don’t know if the Ultraman rumor is true or false (Gunn worded that response in such a way that UM could still be the secondary villain and he’s just not confirming it). But at least his latest post does confirm that Lex will be the central bad guy here and not a villain off to the side like some have speculated.
Anyway, if Ultraman is in this and is a clone, I feel like that takes away some of what makes Ultraman interesting. While yes, at his core, he’s just an evil version of Superman, I think what makes that character (and the Crime Syndicate) appealing is the evil universe he comes from. Justice League: Earth 2 portrayed this brilliantly by showing how Ultraman’s world is inherently evil to the point that even characters who try to do good in it ultimately turn into full-on fascists when they achieve their goals. Additionally, I like how Ultraman and the others aren’t just evil copies of their JL counterparts; they are often different people or have wildly different origins. Ultraman was Clark Kent, but this version was a human astronaut who gained powers by exposure to kryptonite. Owlman is Thomas Wayne Jr.; Bruce is dead. Superwoman is actually Lois Lane. Those twisted origins make those characters more fun. I’m personally sick of multiverse shenanigans but I would rather see the Crime Syndicate than have Ultraman essentially be a handsome version of Bizarro.