Is it permissible to divide profits equally between a sales employee and another colleague who buys products from the former's company at prices set by the administration, and then sells them to his own customers?

Your friend is not permitted to engage in buying and selling during official working hours because the employee's benefits during this time belong to the company. However, he is allowed to do so outside of working hours. Similarly, you are not permitted to take a commission for your official work unless authorized by your employer.