There are many aristocrats acting as minister, ambassador, member of the Assemblée, Prefect or Mayor.
Victor-François de Broglie, 8e duc de Broglie (the father of this Nicolas de Broglie who started the lawsuit for the ducal title) was Mayor of Broglie and was vice-president of the Department de l'Eure (Normandy).
Nicolas' uncle Jean de Broglie, prince de Broglie, was a minister in four Cabinets. He was assassinated in 1976 by an extreme right group holding the Government responsible for "herds of blacks invading France".
https://www.franceinter.fr/emissions/affaires-sensibles/affaires-sensibles-07-decembre-2016
Valéry Giscard d'Estaing, the former President whom recently passed away, belonged to the haute bourgeoisie. His widow Anne-Aymone is noble: a daughter of a comte Sauvage de Brantes and of a princesse de Faucigny-Lucinge et de Coligny.
Another still alive widow of a former President is Bernadette Chirac, also a noble as a daughter of a baron Chodron de Courcel and of a comtesse de Brondeau de Uretières.
Former President Nicolas Sarkozy is born as Nicolas Paul Stéphane Sarközy de Nagy-Bocsa, nobility from Austria-Hungary. It shows that in the Republic the nobility still is apparent in the veins. Especially in the military, the magistrature, the prefecture, the diplomacy but also in politics.
The system of the Grandes Écoles is helpful for the next generations of the "us knows us". Let us say: a De Broglie easily enters this highway to the prestigious institutions of the Republic. Someone in a concrete block in a banlieue can only dream about it.
But of course you are right: no one is appointed as an Ambassador because of having a title. Not even monarchies do that, let alone republics.