RENURPP
My reply was tongue in cheek to other respondents.
The ATC'er knows relevant IFR traffic and their level. the Dash 8 pilot doesn't necessarily on CTAF. If he is passed a Dash 8 onto me prior to my descent and said "climbing to flight levels" it would be completely inappropriate and require more discussion.
I think it was a few years ago (on a depressingly similiar thread to this one) now that I was debating that very scenario with one of your colleagues.
If you're opposite direction traffic to someone in and out of a CTAF it is almost always going to require further discussion with that pilot regardless of whether that pilot is climbing to 5000' or FL210 or "flight levels". So it really doesn't matter if the said pilot (or ATC'er) says FL180 or "flight levels". If you're in G space, you're going to be having a detailed and repeated conversation with that pilot on distance, height, etc, so that you can arrange separation until you're satisfied that you're "well clear".
DIVOSH!