I've never really thought about it. We don't do vaginal penetration during my period, but I use a menstrual cup so he can't tell I'm on my period unless I tell him or he sticks his finger way up there, and then he can feel the base of the cup.
Is this an acceptable practice or does it shock people?
Just depens on who you talke with, weather it is acceptable or not. I know that in the military when a guy goes down on a woman that is on her period the ear what they call red wings. Some people like it others dont it is more of a personal preference to what you like, and if you would want anyone going down on you then?