T4nking Ethics Question: Filling Out Benches

There is a team in my league that is rebuilding and looking to get the #1 pick this off season. Another league-mate mentioned to me that the tanking team does not have their benches filled out (only needs 2 players to fill out his bench), and that this is a form of unethical tanking. I'm the commish so I'm just reaching out to see what is the norm for this. Should teams be mandated to fill out their benches or no? Thanks!