Nick14 was responding to Mr. Horgy's post at the top of page 2.
What he meant was that the Thomas Cook, FlyBe, XL.com and NetJets cadets at OAA are chosen by the airlines and given a conditional job offer before they start training. This makes them off limits for BA recruitment via their SSP scheme, which occurs near the end of or even after completing OAA's integrated course. The assumption is that the cadet programmes soak up the "best and brightest" wannabes, which will eventually pressure BA to compete for them on the front end of the course instead of the back end. Multiply the effect by the 3-4 FTO's BA recruits from on the SSP scheme, since the other FTOs have cadet schemes as well and it could well be putting pressure on BA.
Clanger32 points out however that not all of the best and brightest necessarily care about locking down a job on the front end, so perhaps the pressure on BA is not as strong as Nick14 implies.
The truth probably lies somewhere between the two positions. I suspect the Baby Boomer retirement bubble that is predicted to hit BA in the next decade has more to do with why they might need a cadet programme, but the cadet recruitment competition for the high aptitude wannabes is probably a factor as well.