I do not accept the assertion that prospective employers discriminate against modular graduates and that is based on the fact that I fly with many good co-pilots from both training backgrounds - the split seems to be about even I'd say!
It obviously varies from airline to airline. It sounds like DHL still have an open and fair recruitment policy in which both are equally likely to succeed in. It is a shame though airlines like easyJet don't see it that way...
Which school did your son do his training at in the end?