I just had to read your question after seeing the title.
I'm not a nurse yet but I AM a woman.
I work as an aid and I frequently have to "handle" men's private parts to help them with bathing. Here is how I usually handle it (so to speak):
"Would you like to wash the front and I'll do the back, or should I do both?" So, basically, I just ask, and act like it's no big deal to me either way.
Perhaps in a situation where they require some hands-on help, you could say, "Are you ok with me showing you, or would you like me to get a female nurse?" If you ask like it's not a big deal, they'll probably just tell you. I think a new mom who is uncomfortable will tell you if you ask, especially if you open the door for it. But if they don't mind, then it will save you the time of having to go get someone.
Since it is just touching/helping in a professional manner, I don't think the husbands should care.