I love the EM-1 for land photography. We haven't taken it underwater yet so I can't speak to that. If I were buying a camera for underwater use I'm not sure which way I'd go between the EM-1 and 5. It seems to me that most of the advantages of the 1 such as better autofocus with 4/3 lenses, faster shooting and better ergonomics, don't really apply underwater. But, if he's also planning on using the camera on land, then I would definitely go for the 1 over the 5.
We have recently bought a housing for our EM-1 to replace my wife's EPL-2. We are going to sell the camera body as well as the Olympus housing, Zen dome and macro ports and a tray and handle. We're going to throw in the kit lens that came with the body, but we're keeping the wide angle and macro lenses as well as the arms and strobes. If you're interested please let me know and I'll post some pics.
I don't think we need a new forum, but I suggest that the one we have should be renamed. Mirrorless cameras are not slrs and they aren't point and shoots, so I don't know where to post mirrorless camera stuff. Perhaps the slr forum should be renamed "Interchangeable Lens Cameras".