I have never really been into clash of clans coding or exploiting, but I can't imagine it NOT being possible. For the people that know World of Warcraft, that game is also server sided, yet it's able to dupe items. Not sure if packet editing works (I seriously haven't looked into it), but by using scripts infinitely looting a gem box could be possible.
In the past there used to be 2 major Gem exploits, but these were exploits with the in-game store itself (temporary). Both got patched, and people that used these exploits got their village rewinded to before the exploit (most lost about 1 week of legit playing).
These are exploits with Clash of clans itself.
It think all the easier to do 'gem bugs' are google play refunds or itunes refunds, which have nothing to do with bugs in clash of clans itself.