Azure DevOps Service is a hosted version of Azure DevOps Server (TFS).
Currently it is not possible to connect Azure DevOps Service using O365 GCC account.
But if you have O365, then you can use it to connect to Azure DevOps Service. Meaning you should be able to create an Azure DevOps Service Organization to manage your projects and add other user from your company who are also using your O365 account.
Azure DevOps Service requires a Azure Commercial or Public Cloud Tenant subscription using either Enterprise Agreement (EA) if you are a company or Pay-As-You-Go Azure Subscription on Azure Public Cloud.
It is currently hosted on Azure Commercial Cloud and at the moment there is no road-map to also make it available in other Azure Clouds like US Government cloud. However one can still use O365 account to connect to Azure DevOps Services.