So, as stated in an earlier post, I'm using Unity3D to develop Oh Captain!. I originally used Microsoft's Mixed Reality Toolkit package, but then, of course my project crapped out on me, making corrupting all the scripts I use. Of course.
I switched the project over to the fantastic NewtonVR asset and everything's worked perfectly since! It runs with SteamVR, but the WMR headset works fine with it. Plus I can publish to Steam, a significantly larger platform than the Windows Store. If you're developing for VR in Unity, I highly recommend NewtonVR.