this is a bad idea, as described problem exists even at the moment, and you have described does not work: the inclusion in the WPF application SlimDX an error designer after the first compilation. This bug is also in the examples that come with SlimDX SDK
Make sure you are using .Net Framework 4.0 and not the client. Also instead of AnyCPU specify the explicit architecture i.e. x86 or x64 of the slimdx dll.
A working solution would be to completely abandon the inclusion SlimDX in WPF application. This agrees well with the exact same well-organized architecture of your game engine.
Same issue here.
Using AnyCPU configuration on an x64 system, targeting .NET 3.5..
I have a working solution for Wpf and SlimDX (currently only for Directx11) - if you need it where I will publish the realties