Hi,
Sure, perfectly possible. You can have a datasource that points to another SharePoint server.
By publising your reports and datasources to your new SharePoint/report server (I suppose you are using Reporting Services in SharePoint integration mode), it will just work.
One thing to note (though not a concern at this stage):
In the 3.5 coming version, amongst other features, we will be providing greatly enhanced Rolling-up performances by taking advantage of the object model when reporting services is installed in SharePoint integration mode. In your specific scenario, because you will be adressing another server, you won't be able to take advantage of this specific optimization.
Regards,