Don't know if you saw this yet but this is not working 100% because of.. well. maybe a bug/misfeature in AMXX... This will render some run time errors in server console but really the features of the plugin should be intact. Just looks a little ugly in server console, but don't mind that for awhile ok? :-)
Edit: added cvar hearena_mustusenades, defaults to 1, set to 0 and you can use any weapon but will still get lots of nades.