When GHOST's tasking capabilities are employed, there is a high chance that multiple threads do MPI calls. In this case, an MPI implementation supporting MPI_THREAD_MULTIPLE is required. Otherwise, any MPI-2-compatible implementation should work. There are known problems with Open MPI 1.8.5, cf. https://bitbucket.org/essex/ghost/issues/284/
GHOST has only been tested with SCOTCH 6.0.0.