He's making the right desician. A big part of why is that the version of "Bat Man" he's using is too grounded in pseudo-reality to work for such a crossover. Generally speaking it's the high-camp aspect of Batman that allows him to deal with and play the game alongside other heroes. Nolan's Batman is using things like military prototype weapons that are supposed to be like one generation ahead of current tech, combined with his training. The comic book Batman uses technology that would fit in with Star Trek or Star Wars when the need arises. The higher the level of the opponents, the more crazy Batman gets with the gadgeteering. As I point out a lot of the time, he's not some ordinary guy holding his own with these "post human gods", his capabilities are just as amazing as theirs are. On a fundemental level him being involved there is no more unreal than Lex Luthor being Superman's Arch enemy all these years, Lex is also an "ordinary guy" though his science is hardly ordinary. I've heard some people argue, especially during the old "Tower Of Babel" storyline that Batman is arguably just Lex Luthor with a couple of black belts, at least in the comics.
To do the crossover you'd first need to establish Batman more into the domain of pure cheez as far as the science goes. This would include rebooting the entire franchise to have Batman not just be a kung-fu master with stealth skills, but also to be a penultimate scientist. In the comics Batman does not use people to develop tech for him because he has to, but because it's useful. Batman is crazy powerful because while "ordinary" he's pretty much defined as being the pinnacle of human achievement in everything, except for maybe science where he exceeds that. He analyzes enemies himself, and sits down and kit bashes super weapons as appropriate. "Tower Of Babel" had him personally developing weapons to disable his Justice League teammates if the need ever arose (since he'd only have a chance if he was ready ahead of time), the plot revolving around these prototypes which he never told them about (since they needed to be a surprise weapon) being stolen by Ra's Al Ghul, when Talia got into the Bat Cave via the Teleporter in the Justice League watchtower. This included things like a bullet that vibrated so fast that if "The Flash" tried to vibrate through it it would reverse his own vibrations and trap him (gogo Lex Luthor).
You'll notice that in DCUO Batman is using powered armor in the intro movie, and this was also the case in Frank Miller's "Dark Knight Returns", when he actually fought Superman. I believe it was also briefly mentioned that in that version "The Batmobile" had been augemented with Alien tech.
Also for those who have only heard about it (and a complete side point) Batman also did not win the fight with Superman in "The Dark Knight Returns". The powerful thing about that story is that Superman appears to lose, but you find out later that he threw the fight. When Batman apparently KOed Superman and collapsed from Cardiac Arrest (using a drug to feign death), Superman points out to Robin at his funeral that he was actually conscious and could hear that Batman's heart hadn't fully stopped and pretty much let him go. People tend to forget that entire scene which is what makes the entire story, and is also why "the Dark Knight Strikes Back" is viewed as so much garbage.
As far as movie plots go, I am hard pressed to think of a storyline where Superman would need the movie version of Batman for assistance. In the comics it works because despite what some people "argue" they are actually on very similar power levels overall, just in differant ways (again, think Lex Luthor who has been winning rounds against Superman pretty much forever, even beating him at times, but inevitably having to let him go). That's not true in the comics, honestly Superman would be better to get Lucious Fox to help him in the movies than Batman, but even so the tech isn't really all that high a level. If your doing Superman as per the comics, where Superman is ALSO a scientific genius, and master of Kryptonian Technology (the guy has been building robots since he was Superboy) it's even more of a joke. Batman in the comics can make better toys than Superman at his best, but Batman in the movies is unlikely to have anything even remotely close to what you'd find in "The Fortress Of Solitude" and what Superman learned there.