I was always confused by this place too. I went again last month and flat out asked the waitress. I asked her if it is a tipped position since the layout of the restaurant confused me. She told me that it's up to my discretion.
I'm going to guess....and this is JUST a guess, that they are on a normal hourly pay. Probably $8 an hour or whatever minimum wage is. But also accepts tips. My DD worked the summer at a pizza place like that. Customers came in, placed that order at a counter and then sat down. She would bring their pizza and get them refills. Some people left her tips and others didn't. She made minimum wage (not the lower hourly that full servers get).
In any case, I tipped her at Wolfgang and will now continue to do so. I will say this, I only tipped $5 which was under the 18% minimum that I would normally tip. So I would be curious to know what hourly rate they get paid.