Danzou is to mandara what Darth Sidious is to Senator Palatine.
Honestly at this point I don't see how there could be any debate that Danzou isn't Mandara and it kind of makes sense in that he'd be playing both sides. Just like how Palpatine had the entire separatist fleet run to Coursesant just to kidnap himself to secure his innocence Mandara sends pein to konoah so he can finally take power which makes getting naruto a lot easier since he can keep him in the village and limit his travel.
If you need any other proof take a look at these two manga pages.
http://www.onemanga.com/Naruto/397/03/
http://www.onemanga.com/Naruto/455/17/
They both have the same hair style. If that's not enough proof in manga terms I don't know what is.