Is it possible to include the data from 3rd party extensions into the export profile?
Yes, the Export Orders extension provides the functionality to set connections with third-party extensions. To create such connection, navigate to System > Export Orders > 3rd Party Connections > Add New Connection and fill in the fields according to the guide:
Based on the configuration in the above screenshot, the order_id field is joined with the entity_id field from the foreign table pref_amasty_rma_request, and we can include it in the profile from the Order tab: