Sorry to say, it's a bit of a crap shoot. Some servers are more prone to "play" with you if you express a willingness to play along. Others are more inclined to zero in on the shy and quiet and gently embarrass them into loosening up. In fact, those servers tend to loathe customers who walk in with a self-drawn bulls-eye on their heads, the ones practically screaming "Make fun of me, please!" Kinda like the guy in the comedy club who keeps shouting out random topics to the comic onstage, thinking that he;s somehow "helping." Some servers will stay in character all of the time no matter what, and others just won't. Last time we were there, our server was young, first-generation Asian, and spoke English as a second language. To quote the brilliant sage "Not that there's anything wrong with that..." but our server probably never saw any of the shows the restaurant uses as a template, and had to concentrate very hard on his English just to get the order right. If memory serves, he was there on a CM exchange program. Great guy, wanted to do his job well, and as far serving goes, he did a fantastic job, but he was not a performer and didn't seem to understand the dynamic of the restaurant. My wife and I took solace in watching other people get goofed on by their servers.
My advice is to be as friendly as you would towards any server, and treat them a little more familiar than you might normally (after all, they are supposed to be your mom/dad/brother/sister/crazy aunt/etc.). If they have an acting bone in their body, let them do their thing and then roll with their punches. After all, they ARE the pros and do this for a living. If they aren't performers and you try to force them into being performers it'll just be awkward for everyone (I know, you'd figure anyone working there would be a bit of a ham, but it's not always the case, to paraphrase ol' Rummy, sometimes you open a restaurant with the CMs you have, not necessarily the CMs you want).