I understand our mixed fleet crew in BA who are part of FTC, or Future Talent Crew, have a mentoring process. During the year or so to SCCM under the FTC programme, constant '360 degree feedback' is used along with IFAs or inflight assessments to develop the FTC. I'm not sure if there is an official mentor assigned.
For pilots, many airlines running ab-initio training schemes have a mentor pilot assigned to a course. Usually from the associated airline. Again I'm not sure of the exact set-up.