Azure Policy lets you audit the compliance of the configuration of Azure Resource Manager (ARM) properties. In some cases, such as AKS or Guest Configuration, it can also audit configuration of Resource Provider properties. While Azure Policy can be used to audit how a role definition is defined (sample here), it isn't for applying roles to specific objects. That's the domain of Azure role-based access control (RBAC). If you want the group "Azure Cross Team Contributors" to have access to all resource groups within a subscription, an easier alternative is to grant the role assignment at the subscription scope.
You mention "Resource Group Contributors", but I don't believe there is a built-in role with that name. Is this a custom role you've created?