can dedicated host be shared between different subscriptions created for the same tenant?

DK 

You are correct that subscriptions in Azure are not associated with Azure roles like contributor or owner. However, when I mentioned "adding subscription B as a contributor or owner to the resource group that contains the dedicated host group A," I was referring to adding a user or group in Azure AD to the resource group and assigning them the contributor or owner role.

In Azure, resource groups are used to organize and manage Azure resources, and you can assign users or groups in Azure AD to roles like contributor or owner at the resource group level. By adding subscription B as a contributor or owner to the resource group that contains the dedicated host group A, you would be granting users or groups in subscription B permissions to manage resources within the dedicated host group A.

So to clarify, you would not be adding subscription B itself as a contributor or owner to the resource group, but rather users or groups from subscription B that you want to grant those permissions to.