I'm not an Oly lens maven, but in general an 18-180mm would not be the best choice for UW as it is a zoom telephoto and has really too large a range for UW, IMHO. Telephotos don't work because you're too far away from the subject and putting too much water between you and it. Great for a walking around lens though.
Figuring out ports and lenses is hard, especially in a camera so new. I would say our standard port should accommodate 30-60mm & macro lenses or so, our long port the macro 105mm, and the dome port wider lenses down to 15-11mm (short focal length might be better with a diopter). But we also have an extension ring to lengthen the barrel for longer lenses. It's quite possible that the long port with an extension ring would accommodate the 18-180, but I don't know why you'd want to use it UW.
Jack
Figuring out ports and lenses is hard, especially in a camera so new. I would say our standard port should accommodate 30-60mm & macro lenses or so, our long port the macro 105mm, and the dome port wider lenses down to 15-11mm (short focal length might be better with a diopter). But we also have an extension ring to lengthen the barrel for longer lenses. It's quite possible that the long port with an extension ring would accommodate the 18-180, but I don't know why you'd want to use it UW.
Jack