For me, the key is if the men are being asked (by society) to do the same, and whether women feel compelled to dress a certain way - e.g. do they feel shame if they don't dress the way society is telling them?
Men are simply not expected to show all for swiming. They do not have to do a time-consuming beauty regieme to get rid of their pubic hair and make sure they look "beach ready" - they simply put on swim clothes with sufficient coverage and off they go. I mean, I'm sure some men enjoy wearing skimpy shorts and wax their pubes. But they have a choice - no one judges them if they don't.
Women, on the other hand, are expected to wear clothes that reveal more intimate areas of our body where pubic hair naturally grows, but to remove every trace of it. And we often feel shame if we don't - just look at thsi thread for example - many women are worried they'll be judged for wearing a swim dress.
So, yes, in our society at the moment, a swim dress absolutely is a feminist statement IMO!
(But, if society was telling us we had to wear one and be ashamed of skimpy swimmers, then the opposite would be true. Context matters.)