I know the manga , i know he put the 4th mizu under genjutsu .... and ?
we dont even know if Tobi is a real Uchiha and it was stated that Itachi tsukiomi cannot be broken unless ur is sibling. And Izanami would work even on Tobi , genjutsu master or not.
tskyomi can be broken by the laws of genutsu and since tobi has a sharingan he can fight back it all depends on the user.
samething with sasuke people said well sasuke had tskuyomi ann with that only relatives could break his, well it didn't happen that way since bee had the abilty which was one of the laws to break genjutsu which was to be a perfect jinchuriki.
basically if tobi can use his sharingan to reverse the genjutsu than he would have a chance of breaking it because those are the laws of genjutsu,itachi was most likely lying to sasuke like he was doing before he died.