Did you know if JAR template supports 6-motor drive train?
Yes, it does, and this is shown in the screenshot below from the main.cpp file from their github repository.
Did you know if it is legal to use this template to code robot for competition?
Yes, JAR template is completely competition legal. My only advice would be to attempt to understand the program behind it so that you can better explain the program to judges.
Here’s the qna that specifically answers this
https://www.robotevents.com/de/VRC/2023-2024/QA/1582
Excellent! Thanks for pointing me to the right reference!