Vela or vella is used for a person who is free, jobless, who's just roaming around. The word is mostly used in lighter sense, as in, it's not exactly a replacement for unemployed.
Vele or Velle is plural for Vella.
The meaning for the line Assi vele, sab vele, aa vela ho ja re from Student Of The Year would be "we're free, all are free, come (with us), be free." And 'Sanu velle kende, saanu kee' would be "They call us jobless, how does it matter to us."
Check All Lyrics, Meanings and Translations from Student of The Year HERE.