It's the "smell" that cedar gives off that has been linked to respiratory problems. They may chew wood, but they will not ingest it. And in any case it wouldn't hurt them any more than any other wood if ingested. I keep my rats on non pine/cedar wood shavings, and aspen is quite popular as well.
At any rate, being cedar it will ALWAYS smell of cedar, and the more they chew, the more oil it will leach into the air. Plus if they do sleep in it, then they will be exposed for long periods of time to the oil. So I would avoid cedar houses. The little houses I've used are made of fir or plastic. The plastic ones are FAR easier to clean. And frankly the rats don't seem to care either way. Also I've found that well socialized rats prefer to either sleep in hammocks, on TOP of the houses, or inside a nice tissue box. I've got a wooden house, and a plastic "igloo", and the only guys that use them are baby's I bring home. My lone female really loves the 2 liter soda bottle i cut the end off and tied to the side of the cage on the second level. She pretty much sleeps in that, or the dollar store basket I zip tied high up for a loft.