At the moment we only have access to version 8 of the Lightweight Grid (i.e. version 8 of the Mathematica kernel). Is it safe to run version 8 subkernels together with a version 9 main kernel? It does appear to work, but I am not sure if things can go wrong in unexpected ways.
(For safety I use a v8 main kernel for these calculations, but I since everything seems to work with a v9 main kernel as well, I was curious if this is actually supported.)