As far as contacts removed to the extent that he only sees blobs, I can not imagine anyone being Mattir such a thing. The guy sees the color and knows what it is. If that is not Hirhur inducing, what is? Is this really ligher than Bigdei Tzivonim?
There is also another issue. The mere fact that someone breached something like this and is very aware of the situation that he is in, causes Hirhur. This would apply even to a blind man. You can compare this this to Negeea while under the influence of an externally numbing drug.
The Kalus Rosh theory does come in to play if they are there together as a group. Otherwise, you can not say that the people at the site are in engaged in Kalus Rosh together, because they are not doing anything together per se. However, even with very Tzeniesdike bathing suits, at best it would be like doing exercise in a group, which we refrain from doing. These are expressions of the body and just as mixed dancing is Assur (even according to oomis, I think), this too would not be any better.