I confirmed with customer support working through the GCCH SSO Config with us and my account rep before we did our upgrade that Smartsheet WAS compatible with GCCH, which is why we kept Smartsheet. We have now having issues connecting to OneDrive/SharePoint and looking at the backend configuration, it looks like premium apps are kind of independent from the actual application instance.
Can anyone who is on GCC High, confirm they can use all Smartsheet functions and features has any other user/company not on GCCH?