Unfortunately, ILMerged Rebex DLLs have been reported not to fully work and this is not a supported configuration. Some clients have succeeded in using alternative commercial tools for this (many obfuscators support DLL merging and some of these reportedly handle Rebex DLLs without issues).
I'm not sure I understand the second question. Just reference Rebex DLLs (use NuGet if you prefer) and call Rebex methods the way that best suits your project.