Gambling is a bit of a tricky topic, one in which nobody can win (pun intended).
So here’s our stance:
With the next patch, dropping on May 5th, there will be an explicit rule making it clear that gambling and games of chance are not allowed, to avoid any confusion. However, considering the fact that this kind of activity is considered illegal in certain jurisdictions, we already consider it a violation of our T&C, particularly §13.1 (Users are obliged to…(…)comply with applicable laws and all rights of third parties when using the Services.), and have to step in.