Both traditional and verb-based routing cannot be used in the same ApiController
Original discussion here: http://aspnetwebstack.codeplex.com/workitem/184
We are looking at having better support for this, in part by making our action selection logic easier to extend.
I've written a blog post showing both types of routing working in the same ApiController. It's supported with out-of-the-box WebAPI. http://blog.appliedis.com/2013/03/25/web-api-mixing-traditional-verb-based-routing/