I've only done this a couple of times, but one option is to smoke your ribs on the wsm until they look the way you want, then foil and finish in the oven while you smoke the chicken. (I quickly swap out my foiled ECB pan for the Weber OE pan and add hot water to it for smoking the chicken.) You might want to use a sauce or glaze like Danny Gaulden's that you can simply paint on the ribs after they're done in the oven.
If you decide to do both at the same time on the cooker, I'd cook low-n-slow somewhere in the 250-275* range, depending if spares or backribs, water in the pan, ribs on the top rack, and put the chicken on the bottom rack sometime mid-cook, depending on what exactly you're cooking. If needed, you might just add one small chunk of cherry or apple to make sure the bird gets some smoke, too.