The names woods are marketed under can be misleading and confusing.
The kind of cedar that some people say may be toxic to some critters is the kind used for shavings, which is Eastern Red Cedar, or Aromatic Cedar. It's actually not a cedar, it's a juniper - Juniperus virginiana.
The kind of cedar that fences, siding and shingles are often made of and that you're probably considering for a hive is Western Red Cedar, a different species, Thuja plicata. It's not a true cedar, either, but'll last longer than you will, and like a good wife it's light and stable.
There won't be a toxicity problem with "cedar". Western Red Cedar doesn't give off the fumes that Eastern Cedar does. Besides, hives won't have nearly as much surface area as shavings do.