Tip just like you normally would; good service should be appreciated, even if the food comes directly to your table.
Even though the servers don't bring food, they still take drink orders, and check in on you for other requests, as you noted. Moreover, they should be checking in and making sure your experience there is a good one. They also have to answer when people hit the blue light button, which takes extra effort. Also, you can order off the menu, so they do run food orders just like other restaurants. And, the Blue C in U-Village has a bar section, so those servers bring food as well.
But servers at any place that seats and serves as many children as regularly as that place does deserves the tips, in my opinion. Servers generally split tips with bussers and hostesses, so tipping lower than you normally would affects all of them.