I don't know much about life in the United States Army but I'm pretty sure this is against orders. Really, just about anything that is illegal on or off post is frowned upon as committing a crime is a violation of the oath of enlistment.
in New Mexico though, Border Patrol agents actually did board a school bus and they were within the scope of their duties in doing so. They can and will check any vehicle passing through a checkpoint and, sometimes, elsewhere.
As a record summer heat spreads over the United States, we have a story today about migrants treated for hypothermia after being rescued from the Rio Grande.