This is a question which is not really included in any Ariba guide.
It seems once you activate SSO in ARIBA all your Ariba users will need to use SSO, when you do not really require it for all your Ariba users.
Having Ariba SSO activated we may have these scenarios:
If activating Ariba SSO forces to use always SSO access for all Ariba users we will incurr in SSO additional costs for all Ariba users when we do not really want to apply SSO for all scenarios.
Is there a way to implement Ariba access with SSO for some users and with-out SSO Ariba access simultaneously?
SAP Ariba has multiple solutions, and I do know for SAP Ariba Network (Commerce Automation + Supply Chain Collaboration) does have an option to not "force" SSO login, which means users can log in using SSO and the traditional username and password.
I would suggest opening an SR and check if that can be done the same on your solution.