The OpenAPI add-on does not run any scan rules, thats not its purpose.
Its purpose is to read an open API definition and to add that to the Sites Tree - thats ZAP's internal map of an application.
ZAP will run any passive scan rules you have installed and enabled against it as it is imported.
ZAP will run active scan rules against it only if and when you run the active scanner.
We deliberately split exploring and app from attacking it to give you more control and flexibility.
Cheers,
Simon