Not directly but you can build a C++ DLL that loads .NET and calls the C# dll. The only issue there is the fact that for some odd reason loading an assembly file only works with an absolute path which makes things a bit messy doing a direct approach. So you'd probably want to manually load up the dll into memory and then load the assembly from memory rather than a file.
C# assemblies (DLLs etc) are compiled into CIL, JIT compiled to resolve some late dependencies, then ran on the CLR, so no, they aren't machine code and they won't natively interface with machine code. Even if they could I would throw serious concerns about calling conventions.
