I have been asked by providers if there is something in particular that they should wear.  Many will try to make the experience as enjoyable as possible and understand that how they dress can really get the session off in the right direction.  If they do not ask, I think you should feel free to ask.  Many reviews will say that she was wearing what I had requested.

A certain type of lingerie should not cause too much of a problem even if she is doing outcall.  She can dress conservatively enough not to cause a stir, but once inside can satisfy you wishes.  Not all providers may have a specific outfit and some may not want to pay to obtain it for new a client.  Return customers sometimes get a little better treatment in many aspects and wearing a certain outfit should be one of them.

I have been told many times that unless you ask you will never know.