US citizens are not allowed to participate.
It is because if you accept American customers, you accept American jurisdiction over your entire organization, which means that if you fail to follow their regulations you have the possibility to be in prison. This is why some ICOs doesn't accept US citizen due to this rule that they are implementing.
Except what you described is more or less known as money laundering as is illegal in most parts of the world and will get you and that person in jail
Yes, in this case the laws of not only the US, but also of other countries will be violated, and the mentioned prison can become quite real
Only US-citizens are not allowed to participate in the ICO. All other users can participate