Can Amex offers be activated on multiple cards?

Yes.

If more than 1 of your cards has been targeted for an offer, Savewise is able to activate the offer across all eligible Amex cards.

Here's an example:

Let's say you have an Amex Platinum, Amex Gold, and Amex Green card.

There's an offer for Blue Apron on your Amex Platinum and Amex Gold cards, but not the Amex Green card.

When you activate your Amex offers using Savewise, the Blue Apron offer will be applied to your Amex Platinum and Gold cards.