Is the money of a suitor who works in the administration of mixed university restaurants permissible, especially if he is unable or unwilling to denounce the mixing? And would he be accepted as a husband?

If the suitor is pleasing in his religiosity and character, and his work in managing university restaurants is permissible, then he should be accepted. The mixing of male and female students does not render his work unlawful, as long as his work itself is permissible and does not directly aid in this mixing. He should, however, advise those in charge of the university to prevent unlawful mixing.