I'm not aware of a documentation that describes whether it is safe to attach a VMFS5 LUN to an older host. Personally I would NEVER present a data LUN to a system which doesn't support the file system. I'm not familiar which your storage system, but from my experiences with several other storage systems, I can hardly believe that it isn't possible to configure the proper presentation on it. There's got to be a way to do this.
André