On my Stratus, I have the Comets that came on it. They only have the tinyest bit of tread, a crosshatch actually. I have never had a problem with traction. However I do not ride in the rain, the only wet I ride on is bike paths that have lawn run off on them. My trike has Swalbe tires that has some groves on them but are mainly smooth.

IMHO a tread that is deeper would not make much difference if you hit a patch of sand or gravel while turning. The only thing is to watch where you are riding. Smooth tires are just fine for bents since you probably wont be riding single tracks with mud and loose dirt.