Use SSO for some domains but not others

I’m starting to integrate Okta with a Gerrit deployment (which supports SAML).

This gerrit deployment will have users from 3 or 4 different companies; mine, which uses Okta for SSO and I’ll like to integrate it with Gerrit as well, and other companies (partners) for which I’d like to provide magic link login (so we can verify that the email address is still valid every time to avoid former employees getting access).

Also, not every employee should have access; we need to be able to deny access (for example, by only granting access to users for which an account already exists).

Is this scenario supported?