Half of Andy Serkis' job portraying Gollum was done by animators, even though Serkis provided the basic facial expressions.

I would've given him the best voice acting award though.

Every last motion Gollum makes was Serkis doing it, including when he's jumping up on rocks and climbing down head-first. The animators certainly deserve credit for the facial expressions and the rest of the work of the digital costume, but he physically acted the part.