Can someone check the bottom text? I can read it, but I'm sure I've got the meaning right.
I interpreted Ｘような、そうでないような as something like "It's like Ｘ, but at the same time it's not"

Wouldn't でない be like 出ない？

I don't have a clue either, but I'd read it as 俺のハルヒが　こんな　に　可愛い　わけ　ない　とは、言い切れないような　そう　でない　よう　な, "There's no reason for my Haruhi to be this cute. Looks like I can't say that, yeah, looks like it won't come out."

I read it as:
"俺のハルヒがこんなに可愛い訳がない
…とは言い切れないようなそうでないような"

Contradiction said:
Wouldn't でない be like 出ない？

Sort of. It could be 出ない, or it could be a contraction of ではない. I think it's fair enough to say you're right on this one, though.

The とは言 (even as part of 言い切) and the rhetorical な at the end convinced me to phrase it like I have.