In this situation when you're already naked and everyone can already see your dick, I don't see what difference it should make to them how soft or hard it is, except a few inches!
On the other hand, being naked with an erection feels like I'm a different type of naked than when I am naked without an erection. The thing is, I really don't know which way feels more naked. When I am soft, the erection is another thing that I am without, in addition to being without clothes. When I am hard, not only is my entire body visible, my arousal is visible as well. This is why I personally don't feel like someone has really seen me naked unless they have seen me both with an erection and without an erection.
Even though being hard in the nude and being soft in the nude are two different types of nudity, I still don't see why it should matter which state other people see you in. But I guess there are a lot of things about society that don't necessarily make sense. Of course this sort of thing is ok in reality, but whether it is ok in other people's minds, who knows. So overall I would say yes, it is ok. As other posters have said, just be cool about it.