It would seem that a hiring policy restricted to a national flight school and the national air force might be considered discriminatory.
For that it is enough that a rule has a discriminatory effect in practice even if it isn't formulated to discriminate. (e.g. a company offering no part-time work although it would be feasible or denying promotions to part-timew workers could be considered to discriminate against women considering that women look for part-time work more often than men.)
IMHO hiring restricted to graduates of one or two national schools and the national air force is also a hindrance to free movement of labour. This can be proved by an imaginary extension of that practice to all airlines. If every airline acted like this your choice of flight school would forever limit you to the airlines accepting graduates of that school.
The national air force requirement is even worse because even if you might be able to enrol in a Dutch flying school as a foreign national the Dutch Air Force will not take you.
While this is interesting in principle one might argue that lessened qualification requirements would not be in the interest of pilots or at least make no change.
"Free access" to the major carriers would put more pressure on smaller airlines to improve conditions to keep pilots (as demonstrated during last year's hiring spree). It would however reduce bargaining power for pilots of major carriers as their companies would have a far bigger pool of pilots to hire from.
Within the present "system" pilots at smaller and regional carriers are forced to stay where they are (or relocate to the sandy/steamy parts of the world) which might induce them to apply more pressure towards better conditions at home. (I.e. having the prospect of spending a further 20-25 years flying a CRJ, Dash 8 or the like I will less likely endure bad conditions than with a prospect of "I'll change to the majors soon".)
It would be quite interesting to see statistics on foreign employment in airlines. Obviously having too few national graduates we employ a lot of non-Austrians here, while other countries seem to be rather closed for anyone not speaking the national language. (Asking the UK pilots: are there many non-English/non-Commonwealth pilots in your operation?)