Hi Michael,
The summary row of GridGroupingControl does not have a support to the behavior of frozen row which can be achieved through some workaround by placing a grid at the bottom of the control with a single row which appears to be a summary for the control.
Please refer the sample attached in the below location:
http://www.syncfusion.com/uploads/redirect.aspx?&team=support&file=FrozenSummary-10671657.zipLet me know if you have any queries.
Regards,
Jisha