Atul,
Are you referring to Work force central integrating with SAP On premise and SAP on Cloud ?
Workforce central can integrate with SAP On premise and SAP on cloud.
I have worked on Kronos/On premise integration using flat files though standard API is avaliable now.
Just started on a project where there is SAP Cloud Payroll with Kronos and we are using API that is avaliable .We are integrating both SAP cloud payroll and also SF.
regards
Harris