Is it possible to connect VIDI X to other boards such as Arduino UNO, Leonardo, MEGA, etc.?

You can learn more about serial (UART) communication in the relevant tutorial by visiting the following link: https://hr.vidi-x.org/radionice/vidi-project-x-92-serijska-komunikacija/. You will find more information on this topic in the section on communication between VIDI X and Arduino.