Amumu is still a yordle, and I can prove it.
In the documentary about the Curse Of The Sad Mummy music video we get a brief (and I do mean brief) glimpse of his doggy ears.
http://tinypic.com/r/35kk02h/9
If you don't believe me then look for yourself. You may need to pause and play the video a few times before you see it.
https://youtu.be/4bQBmAO0hk4?t=2115
35:15 to 35:17
