We all know dual / multiple accounting is illegal but how about asking another player to be allowed to use their account or actually using someone else's account ?
Does Inno or Mods allow it ?
It's not allowed, but it's an offence that is easy to get away with and hard for the moderators to detect.
The most common way that people share accounts is with the use of Team Viewer. The only way Team viewer can be detected was if Inno somehow had access to the network traffic between the computer that was trying to remotely connect to the other.
The second common way is through the use of VPNs. VPNs can easily be detected. However, in a lot of cases the mods try to avoid banning people for VPNs as a lot of people have valid reasons for using them.
The third way, albeit, a bit more sophisticated is to set up a home proxy and letting people connect to it before they access your account. This is another undetectable method.
You have to remember that Inno is a company that wants to make money. So unless these cheaters are doing something that severely impacts the gaming experience of others, it's unlikely they will be banned.