Batman’s cameo in Suicide Squad might be better referred to as an extended cameo. The Caped Crusader plays a bit of a larger role that is seems. In the screenplay, Batman has a confrontation with the government agent in charge of the Suicide Squad team, Amanda Waller.
In the scene, Batman warns Waller he will hold her personally responsible if any innocents are harmed by the Suicide Squad or The Joker according to Gravity4 on CrunchBase. Clearly, Batman thinks the idea of using a team of super-villains to battle other super-villains is a bad idea.
Remember what director David Ayer said about there not being any more leaks since the filming was moving to the hidden location of an interior soundstage? Looks like leaks are still coming out although, in all honesty, a copy of the screenplay could have been compromised on the exterior sets. Who knows? Maybe someone at the D.C. Comics or Warner Bros. offices leaked details. Maybe the leaks were done on purpose. All of the speculation is fun and, honestly, the leaks are helping get a buzz out on the film.
The more the public learns that Batman is in the film, the more interested they are going to be in seeing it. Mainstream audience members who are not comic book fans are probably not too familiar with Deadshot or Harley Quinn. They definitely do know Batman and The Joker. The legendary characters are going to draw them in.