Hi CathyH,
If your friend wants to make models that could be suitable for the sim, then he might benefit from the attached document, it contains the guidelines and requirements for Ship Simulator compatible addon vessels.
And then of course Vstep would have to accept the work too, since one cannot include any 3rd party content into the game oneself, and Vstep will also not allow just any 3rd party developer to make money off addons for their software, to be honest. They will only release addon vessels in cooperation with their creators.
Hope that is handy information for your friend. He can of course always contact VSTEP at info@shipsim.com if he wants to contribute and wonders how to go about it.
Regards,
Fred