It's a terrible decision for a sport and club promoting healthy lifestyles. With alcohol and betting you can say "Drink responsibly" and "Bet responsibly", which many do without becoming addicted.
For people who say "It's just water vapour" it's not. The vapour can still contain nicotine and other dangerous chemicals and metals. You just know that people will have cheap knock-off versions as well, which won't be low vapour and you don't know what they could contain.
A number of e-cigs have even exploded, so the club will allow potential explosive devices, which can damage the health of the user and others but you can't take in your own food and drink