If you see warnings about unsupported elements, you can ignore them:
These warnings are the result of Workflow Accelerator export of BPMN files. A BPMN diagram should include information about swim lanes (laneSet) in order to be used with other BPMN tools. However, Workflow Accelerator itself doesn't use swim lanes that way. These values are ignored during the import because the information is stored elsewhere in the file. The same applies to the documentation elements.
KBA , BPI-SIG-CA-INT , Import / Export for SAP Signavio , How To