Still not sure if you have grasped the concept to be honest.
An ITO or ANSP can, if they want, spend money and have the FEAST programme to evaluate their own trainee ATCOs. They do not have to.
If one ANSP want to set the bar at 98% or 2% that is up to them.
Why would an employer let another company choose their own trainees? They merely pay a fee to use FEAST.
Your suggestion is one of corruption at one ANSP if I get this right. This is not a FEAST issue.