The Air Carrier pre-employment flight eval in the 737 is just to determine relative familiarity and proficiency in turbojet aircraft. It is similar to an airlne interview sim eval. Not a complete PC by any means.
Once you get assigned to an office, depending on your actual position, you may or may not be assigned to do certification work in a particular fleet. If you are assigned to conduct flight checks in a particular fleet, the air carrier will train you in their sims just as if you were employed by the air carrier as a pilot. See FAA Order 8900.1, Volume 13, Chapter 2 for Aircrew Program Manager or Asst. Aircrew Progam Manager (APM or AAPM) positions. These are well sought after positions at the GS-13 and 14 level. There is an agreement between the Agency and the Airline, called an MOU. If you do get to stay current in something, you will get appx 2 hours of sim time each quarter and an equivalent to a 121.441 PC each year (Dash-2) in FAA speak.
Some new hire positions may not require participation in an aircraft. For example, The ASAP Program Manager position at a CMO typically do not require aircraft currency.
Most of your time spent the first year will be getting trained on the 8900.1 and Safety Assurance System (SAS), a complicated software where the actual results of inspections are input. The POI manages the SAS program, and the Supervisor assigns the inspections.