While I understand that paying for the rating is a bad thing, I don't see the problem in hiring them in any other company after they have succeeded in the first place. If they would be incapable pilots, you could read it in the newspapers. I still have to read a statistic that says that paying pilots are worse than others.
All in all, if you have a certain set of abilities, it's indifferent that you paid for it or not. And Head of Ops all over the world wouldn't care if they have paid for it in their previous job.
Which lead to the conclusion: There must be something else wrong why airlines don't get the pilots they need. Airlines only who ask for money to fly for them would experience a shortage. Obviously they don't. As soon as they wouldn't find any paying pilots anymore, they would lift the pay and take them for free. Which they don't do. So: There is something else wrong with the head of operations, not with the pilots!
Your reasoning is not logical and only serves the purpose of blaming self-paying pilots
Dani