I can only give you the anecdotal evidence that Hazelcast has been working just fine in my environments. We're currently running v1.2.2 of the plugin (based on Hazelcast 3.17) on Openfire 3.9.3, but have been using this and earlier versions for over a year now (starting on Openfire 3.8.2). I've never had a problem with messages reaching clients due to Hazelcast, as far as I know. We have had some hiccups when recycling one of the cluster nodes, where clients drop their connections but then almost immediately re-connect.
It would be helpful if we could get some more expert advice on how to troubleshoot Hazelcast on Openfire, as it's not very well documented.