He can listen to the net, if he has a radio, or online, without being a member of the forum. I believe he can get on the site as a guest, though I am not sure if he can post. Pretty sure he can get into chat, as well, without being a member, though I am not sure.
If he is a licensed Amateur operator he can participate in the net without being a member here. If not licensed he can be in chat and participate, I think. Well, he can be in the chat and participate if he is licensed, too.
Pretty much just my opinion, as I am not as sure of the above as I thought I was when I started typing.