We provide a generic API for DLL loading and DLL function binding that is implemented for all supported platforms. The functions you are looking for are:
FPlatformProcess::GetDllHandle - loads a DLL, i.e. what LoadLibrary does on Windows FPlatformProcess::GetDllExport - binds a function from a DLL, i.e. what GetProcAddress does on Windows FPlatformProcess::FreeDllHandle - unloads a DLL, i.e. what FreeLibrary does on Windows
I just wanted to add that you can use FPaths to convert relative paths to full (FPaths::ConvertRelativePathToFull()) and combine paths (FPaths::Combine) allowing you to specify a relative path to your dll easily.