Just as I was getting ready to try and pay my first Amex statement by using Curve linked to my IHG Premium credit card, they release new policies specifically forbidding that behaviour. I was really looking forward to getting double points. I suppose I can let them off as they have finally added Amex access for everyone now.
'Rumour' (aka personal experience) has it that it actually still works fine in practice, or did still yesterday anyway. You would of course be potentially putting your relationship with curve at risk of course, but you may or may not see that as much of a problem.