Yes. This applies to Membership clients only. When you enroll a client in a Membership, you have the option to link the record to an existing Stripe or Square customer record. If the client does not already exist in your Stripe or Square account, a new customer is created when you add their credit card in MassageBook.
Any changes you make to credit cards on file will update across locations. This means that if you add or delete a credit card in MassageBook, the credit card will be added or deleted in Stripe or Square as well, and vice versa.
See the screenshots below as an example, where the card ending in 8210 has been deleted in MassageBook and therefore has been deleted in Stripe:
