Some people might use it to gamble, it is inevitable.
If someone made a bet to his friends and he lost, it is obvious he will be paying his friend money. If he has Facebook coin then he can use it to pay his friends. It is not the gambling you think but that is the only way I can relate it to gambling since most of the sites that I read for some time now says they will only be in their sites.
We know it can't be transacted on gambling sites so I think it is impossible. Also, it is said to be connected to dollars so I think people will not be using it to gamble that much if it can be used.