I am afraid you did not understand me.
inline assembly is machine asm not the MSIL that can be written inside your c,c++ code directly.
As for the main question, NO you CANNOT use native assembly in managed
languages since the binaries are compiled to a high-level assembler which in
turn are compiled to native assembler by the JIT engine upon execution.
You can use(not include) native(unmanged) Dlls in c# just with DllImport attribute you can call any function from any Unmanaged dll,Microsoft has to do that to enable the programmers to use windows API.
You can probably use C++ with Managed Extensions to use assembler but
for most projects I wouldn't recommend it since you'll be breaking that wonderful
cross-platformness that C# has (assuming you have an environment on that platform such as .NET, ROTOR, DotGnu, or Mono).
I don't think he want to make his app cross-platform because of a simple thing shellcodes are not portable like any low level assembly application,you need much work to make it portable.