Di Maulo might have pretended to be neutral, but I seriously doubt he truly stayed out of the Desjardins/Montagna feud. Of course we'll probably never truly know.
I think his "inaction" is what got him killed though. He didn't defend the Rizzuto's, like you said either acted neutral or pretended to (I think the latter) and more than likely helped Desjardins go along and help him with his attempt to take over. Otherwise I think Desjardins would have been dealt with pretty quick without Di Maulo's backing. But who really knows anymore? lol