Different companies have different selection procedures, but broadly speaking the objective is the same, so last Autumn when bmibaby poured 120+ 737 type rated and experienced lots of people had the opportunity to see first hand how it worked, the middle east crowd were very thorough especially on the medical front which surprised a few, BA were their (un)helpful self, Jet2 had the now infamous compass test, Monarch, who i expected to be very much into all manner of testing & sim rides basically had a 50 min chat, no technicals or mind games and Norwegian, again a chat, very informal off the back of an online personality test and followed by a basic sim check for Captains.
My point here is that the result is more or less the same, all of these companies either took or rejected some candidates that raised a few eyebrows for ex baby trainers and flight crew management.
To date I'm not aware of any ex baby pilot (other than sandpit 777, which was always going to be a big jump for some) needing additional training or not making it through the conversion course's
Jet2 could have done a lot worse than adopt the former baby "Durnford" method approach of sitting down in Costa coffee with Jet2 current/present fleet 737 manager and interviewee and have a chat, it wouldn't be perfect, but nothing is?