Well since it's frowned upon to explicitly discus acts, I would say that depicting them is vaulting clean past the line.

Good question.  I've never done it so I can't answer directly, but I did arrange a meeting with a very well established woman via P411 and when I inquired very discreetly to something I might like to try she suggested that if it would make me more comfortable I could just send her a link to a video that depicted it.  I thought it was a very clever suggestion, but in the end I just came right out and asked (I was already verified) since it was simpler and she was fine with my directness.  
In this one instance a provider suggested it, and while  I doubt it's very common, it does happen.

FWIW, my own experience is to start off very discreet and to always be polite.  However once you've established a line of communication and have been verified you can ask (sometimes in a roundabout fashion) about many things.   I've rarely had it go wrong (under 1%), although sometimes I'm too roundabout and they won't understand -- in which case I just speak plainly.   YMMV of course.

and only with permission. It can be very hottt to share a fantasy with your date, but you better be  
a good gauge of what she's open to. So ASK.  

But always AFTER you've been screened.

Once you have established compatibility she will be eager for ideas to please you.  

...it's alright with me.