Dear Sam,
Happy to read, that your configuration is OK now. The OSS support would have help you too.
I suppose that you are asking if it is possible to use SPNego and SNC for ABAP togehter right?
Both can be used in parallel. SPNego for ABAP is designed for SSO using browser application to the ABAP server (NWBC or Web GUI). SNC is designed for SAP GUI and all other RFC connections.
Your use case and your security requirement should define if you want to have one or both. Ther are enough use case documentation in the SAP Single Sign-On under popular content.
KR
Valerie