Pure C is a fine choice, too. As is Objective-C. I'm pretty sure Objective-C will outperform Java and C# both. And there's no question that the best choice would be C, for its efficiency and its versatility.
If you use Objective-C just like C, then maybe. Otherwise, no.
And you'd have to be insane to write a game these days in C. It's just not a productive enough language for that. Whatever little speed you give up for Java pays off many times over in speed of development, debuggability, etc.
It would have disadvantages from the point of view of rapid development though, especially considering his team are going to be much more experienced in Java now.
Would be interesting to know if he is using Scala for any parts of it though.
