As long as it behaves like local storage and gives you the performance you want, Elasticsearch doesn't care. See these docs for more information.
GlusterFS had some bugs that caused data corruption in the past (i.e. it did not behave like a local filesystem) but as long as these bugs are all fixed then it should work. That said, IMO it's pointless to put a distributed system like Elasticsearch on top of a distributed filesystem, and it's still a bit of a risky choice (this filesystem is relatively new as filesystems go, and rather complex, and Elastic doesn't run any tests on it) but it's your data that's at risk so ultimately the choice is yours.