You can nest a comp with ray traced rendering in a comp with classic rendering but collapse transformations may not produce the results you want so you generally keep it turned off.
Thanks Rick, hopefully I can get that to work properly for me...
And thanks for the link Todd, though it doesn't mention anything about the issue I'm curious about...
One more related question... If I turn off the Ray Traced 3D renderer after I've created an object, and then turn it back on at a later point, will it remember the settings of the 3D object?