DCAU = DC Animated Universe. As in the Superman, Batman, Batman Beyond, and both of the original Justice League cartoons.
He's the Main Man, a.k.a., the guy Wolverine wishes he could be.
Supposedly, Logan technically won when they fought off-panel during the Marvel vs. DC crossover (which apparently wasn't shown because no one could come up with a believable way for him to do so), but the victors of said battles were decided via a popularity vote amongst the fanbase, so I wouldn't even consider this a proper fight. Like, at all. Word of God say's he took a dive for $50, offered by one Charles Xavier.
*Corrected for clarity.
And who hasn't bested Deadpool at some point or another? Half of his shtick is being the Marvel Universe's punching bag, both literally and figuratively. Just because someone else was able to come out on top in a certain encounter due to plot reasons, that doesn't mean they would necessarily have the same success 100% of the time. If that were the case, then theoretically, almost anybody could defeat Deadpool.
If this page is any indication, I'd say that he and Wade are pretty evenly matched. Doesn't matter how many times you kill either of them if neither actually stays dead. Especially when every blood cell in Lobo's body is capable of individually becoming a brand new Lobo, and then they all go on a rampage and fight to the death in order to become the only Lobo.
Which is great, as it just gives good old D-Pooly an excuse to whip out the Deadpool Corps. And then things can really start getting nasty and ridiculous.