Can I create a workflow to create an inventory adjustment as soon as an item is received? i.e. purchase order delivery creates an inventory adjust from Item A to Item B, and C

It doesn't look like you can create native transactions via "Create Record" in workflows, so probably not. It would need to be scripted. A script could then read from the a custom field or custom record that tells it what item is then "input" (received) and what is the "output" (added to Inventory adjustment).