I never heard about an Amex card beeing cancelled due to lack of use.

If a card account had no activity for long time , and is not linked to any other active account, I would call Amex before trying to charge anything.

If you hold two different IEC accounts (means different account numbers, the green is not a free supplemantary card in your name) , both accounts are linked and it should not be a problem to use the inactive card.