“The procedure entry point… could not be located” in the wrong DLL

This looks to be a bug in Visual Studio 2010 Release mode (Haskell dll functions are not imported by exe built in Release mode hence Haskell dll is not loaded, in Debug imports are present and it works fine).

The same exe project built in Release mode using Visual Studio 2013 Update 4 and Visual Studio 2015 RC works fine.

Have you tried using .def file to define exports? https://msdn.microsoft.com/en-us/library/d91k01sh.aspx

After you create it, you must edit project properties Linker->Input->Module definition file