The way I see it, he's giving a performance which has been captured digitally, but it's still his work, so he should be recognised for it. Many people who have seen the film all agree on his performance - the same as he did with Gollum. His performances made the character what it was. Another actor doing the motion capture would do it differently. It's the same situation as Scarlett Johanssen being ineligible for a Golden Globe for her voice work on "Her", even though her performance has been critically acclaimed.
An award for a performance should be allowed regardless of the type of performance. I don't think any voice-over work has ever been nominated for the best actor Oscar. It's time for the Academy to modernise! At least they should have a separate category for this type of performance as they deserve some recognition.