Can a resource with actuals get added directly as a planned resource to the financial project plan?

Yes. When the Set unplanned assignments as planned assignments check box is selected under the Plan Settings tab in the Manage Project Plan Types page and also for your project.

As project costs are incurred, the resource is added as a planned resource to the financial project plan instead of being marked as unplanned.

If your planning resource breakdown structure allows changes at the project level, then select the Automatically add resources on incurring actual amounts check box in the Manage Planning and Billing Resource Breakdown Structures page. As project costs are incurred, resources are automatically added to the primary planning resource breakdown structure.