If Manu is not injured, Udoka would be sitting on the pine. Manu is injured, thus, either Hairston or Ime needed to step in and provide defense, scoring and efficiency. Hairston isn't fully up to speed playing the wing and defending the way Pop needs it to be. Ime has more experience and is able to play with decent acuity whereever he is needed.
I'm not an Ime lover...I just notice that he is tough-minded defensively, knows where to go playing multiple positions, he can pass and he can score out on the floor on any given night (not just jump and dunk). His 7 quick points and defense helped push the Spurs into their 24-8 run during the middle portion of the game.