I am looking to automate creation of Item Receipt and Cash Refund transactions (via workflow) for RMA's meeting certain criteria. Is this possible only utilizing Workflows only, or does this also require a 'Workflow Action Script'?

I think it would require a custom action script. The action you are looking for is the Transform record action which only works on very limited transaction pairs Like SO to Invoice etc

It was resolved without any scripting, admittedly by a consultant and not myself 🙂. Upon creation (or viewing/editing) RMA, a 'Transform Record' action type is used, and Record Type 'Item Receipt' was selected from a dropdown menu under Parameters.