f2000,
Yes absolutely. There is a large element of "lottery" in these assesments. They are most certainly worth a shot at, because the potential reward is a very good one. However I wouldn't advise your son to put life on hold over them. The first stage only involves a set of "tests." There is no interview element or qualification assessment at this stage.
Presumably he will not be in posession of a CPL prior to the notification from these assessments, so it is unlikely to have any adverse effect.