Given that Frasier and Niles are such regular customers, I should think that most of the waiters/waitresses at Cafe Nervosa know them well - not as friends, obviously, but are fully aware of who they are, especially as Frasier is something of a celebrity, and know them by sight.
I was wondering what they would think of Frasier and Niles. I really liked the waitress (played by Luck Hari) who appeared in a few of the episodes in the earlier seasons. It seemed to me, in quite a few episodes, that she didn't seem to be too glad to see them, particularly with Frasier in "My Coffee With Niles" - well, who could blame her? [:]:-)[/:] Even the way she cut up Niles' card in "Frasier Grinch" - she didn't come across as too apologetic about it to me, she just said it so abruptly, which was I found that bit very funny.
It's kind of hard to speculate on, because there's little interaction between the waiters/waitresses and the Crane boys, but if Niles and Frasier get so fussy about their orders when the tiniest thing is out of place, I wonder if the staff are silently cursing them behind the counter?
I'm also reminded of a season ten episode when Frasier remarks on the cafe being packed, and Daphne explaining that it's her mother's day off, and apparently a mass-email went around informing everyone that Mrs. Moon wouldn't be there. Then she added, "You should see this place when they know you're not coming." She seemed to be referring to the customers in general, but I wonder whether the staff at Cafe Nervosa have any pleasure or pride in having Frasier and Niles as regulars? I can actually picture them saying nasty things about them back behind the counter, but maybe not...