Oliver has a big role to play in the right type of game. As it stands, I'd personally have him sitting just in front of Spencer and Henderson in a midfield 3.
Having somebody behind a central striker who can drop in, create space for either sitting midfielder to go beyond or create a channel for a wide man to cut in is a major asset. Apart from possibly Nisbet, we have nobody who really suits that role. Miller is predominantly a wide player and Lawal doesn't have the brain for it. That's why Oliver is important.