Pal Sarkozy (Nicolas' father) tried to enlist in the Legion after leaving Hungary but was denied entry, from what I've read for medical reasons. So i doubt this is the reason why he was naturalised.
However, this should be taken with a pinch of salt... The current French President's father is kind of a 'shadowy' character and little is known for sure about his life.
He abandonned his family when little Nicolas was still a young boy and has pursued all sorts of occupations throughout his life.
...pragmatic ?? it would be accused of caving in to nepotism of the presidential kind....dead soldiers in cold graves six feet under would turn in them in disdain and with a audible resounding groan in the still of the night of eery graveyards....