Per MSDN, The BizTalk Adapter does not support has several limitations, including a lack of support for ITAB II table types (hierarchical tables):
The SAP adapter does not support RFCs with complex parameter types, including ITAB II (hierarchical) table types. The SAP adapter [also] does not support RFCs having custom ABAP types.
I'm curious if anyone has come up with a workaround for this issue, or if it would require writing wrapper RFCs.
We do not use the BizTalk SAP Adapter, but we do use other third party SAP adapters that have similar issues and the current workaround for us is to write wrapper RFC that maps the unsupported types to the supported types.