Whether your current library can be used in a Metro style app depends on what API it calls. Metro style apps can p-invoke into native DLLs, but the native DLL must be valid for Metro.
If the library calls API that are available in the Metro family then it will work. If not then it would need to be ported. Depending on the library that could be trivial or very difficult. You can try using it from a Metro style app and run the Windows
App Cert Kit against it to see if it passes.
Likewise for C# based SNMP libraries: if they use only parts of the framework available in the Metro profile then they will work. If they use parts which are not available then they won't work. How easy they are to convert depends on how much they depend
on the unavailable code.
Which API are allowed are documented at
Win32 and COM for Metro style apps and
.NET for Metro style apps .
--Rob