My name is Ciprian from Okta Customer Support. Sure, you can have two GStuite instances as Profile Masters. There is no limitation.
In case you'll have a user in both GSuite instances, that particular user will be mastered by the GSuite instances which is on top of the other, on the Profile Master list in Okta (Directory > Profile Master).
In order to set up your second G Suite domain with Okta, with SSO and provisioning, you only have to add a second G Suite application in Okta (from your Admin Console -> Applications -> Add Application); this new app has to be configured using the information from your second G Suite tenant. In this way, you'll have two G Suite applications in Okta, one for every of your G Suite instances. For further reference: https://help.okta.com/en/prod/Content/Topics/Directory/Attribute_Level_Mastering.htm
Ciprian Samihaian Technical Support Engineer Okta Global Customer Care