I am not fullu clear on what your requirements are for your use case but yes App Builder/Project Firefly can call the AEM Assets API. This is of course if the AEM instance is hosted on the public internet and the api end point is not protected by a firewall. I have written actions in the past that used the Assets API and it was pretty straight forward to do.
Project Firefly/App Builder Actions are built using standard nodejs and nodejs has the fetch library for making POST/GET/PATCH/DELETE Rest calls.
I don't see any code labs or medium articles that publish code out there. We are working on more AEM use case sample code as we speak.