This is exactly what my experience was Tuesday night on my non-vanilla date. 80% of the conversation was vanilla, 20% D/s, and the D/s part was in general terms. We exchanged our ideas of what D/s is, and our general characteristics of what we're looking for. He didn't really 'maintain that dominance', but I didn't have that expectation. I actually felt very comfortable and will be seeing him for dinner again in a couple of weeks.
On the other hand, today I have a lunch date. And our one prior interaction, as well as the phone conversations and emails since, have put us on the path to having the limits and boundaries conversation today. And I am his guest at a play-party tonight, if we agree we are a good match today. Our interaction will be vanilla, in that I don't want him to do his Domly thing until we've set up some parameters...but the conversation will be completely non-vanilla.