They would have, yes, but the build up and outcome would be different:
Not invisible
-surprised to see him and apologize
-some probably ask - or even insist - to join him
-Dick offers to leave instead, but they decline, taking his condition into consideration
Conclusion: Dick probably gets to enjoy the rest of the bath, either alone, or with the girls, while his back is turned, blindfolded, etc.
Invisible
-One or more of the girls notices a 'presence', removes the concealment and attacks, or Dick sneaks out undetected(highly unlikely, due to fanservice reasons)
-Dick gets labeled a pervert, on the accusation of 'waiting on them while invisible'.
Conclusion: Dick probably gets kicked out of the bath, with more damage than he entered with, and a new title.
I've seen the latter play out too many times - whatever happens next, I hope the girls are chill about it.