Besides, if they can discuss about Bitcointalk in detail, then I think they will learn about Bitcointalk besides investing in Bitcoin. In this, the person addicted to gambling could stay away from gambling besides earning money.
I would have welcomed this as a nice idea since there is some kind of prestige given to a bitcoin investor more than a gambler even if both are risky. But on a second thought when you talked about introducing this forum to the gambling addict.
Have you checked around and see so many signature and avatar of casinos? This means that with a single click in any signature they are already in the gambling site. Introducing a gambling addict to this forum is setting them up for more addiction.
Even if they are banned from visiting the gambling boards which is not possible. When a gambler becomes a trader or an investor, they will still void the rule of not investing more than you can lose. You will see them going with high leverages and trading futures. It is better to quench the gambling zeal rather than to reclothe it.