Third Party integration to upload data into HCM

Summary:

Investigating upload of external data to Fusion, via a third party product, in order to undertake employee record onboarding and lifecycle tasks, such as the following:

• populate the fields for an employee record (e.g. My Client Groups > New Person > Hire an Employee).
• amend/correct the fields for an existing employee (e.g. My Client Groups > Person Management > enter employee name > Personal and Employment > Direct Reports > populate details)
• terminate an employee record (e.g. My Team > Termination > select employee > populate details)

And with apologies for rudimentary terms, my question: Is there a reliance on HCM front end screens in My Client Groups, My Teams etc. being either classic/responsive, or Redwood, prior to the commencement of any integration tool being established.