elimination of possibility's leads me to the following conclusion:
1) he can't go to the battlefield, just like kabuto could not. he is the one that preformed the edo tensei of the 4 kages, and madara is an uchiha well capable of preforming genjutsu. we know that orochimaru is not invulnerable to genjutsu from his encounter with itachi. so madara could make him undo the edo tensei, it is therefore strategically unlogic for him to enter the main battlefield.
2) also since he is letting the hokage act as they wish he does not require to concentrate on the edo tensei jutsu therefor he is free do to as he likes as long as he doesn't show up on the battlefield.
3) and I agree with some others here, he is not interested in going to heal the kage, we have never seen him preform healing of others. unless he wants to talk to Tsunade, but I think that has a low probability
4) he was at kabuto's location before and had no more interest in kabuto other then reclaiming his power that was present in kabuto. since he already completed this task I see no reason for him to go back.
therefor I can only think of one possible other location that might interest him. Tobi's hideout, and his sharingan collection. it is clear from the manga chapters before that orochimaru knew a great deal about tobi and madara before this war started and he was aware of his work with the firsts cells and the creation of the zetsu army. He knew this since kabuto knew it and he was orochimaru's spy. to me it only feels highly plausible that orochimaru might want to go have a peak inside the hideout, now that it's unguarded and tobi and madara are a bit busy. he might even be the one to get yamato out of the big tree, not that that is his first goal or that he even knows about this already, but it's an option he will have if he goes there
