Well having owned rats I've heard/read more than on here I think, as rats are especially prone to respiratory problems. Some people don't think there's enough evidence (especially as there's a lack of studies done in the UK rather than American studies) but the way I see it is if there's a doubt, why risk it when there are alternatives? Especially as the alternatives aren't really any more expensive - a bale of Ecopetbed or Aubiose runs at around a fiver and lasts ages. Carriage can be a bit more but no more so than pellet litter which is heavy too. Plus on the rat forum I was on, lots of members from nearby areas would pool together when needed and order a palletful, to get a good price, and occasionally the odd generous member would deliver to those who couldn't pick up for petrol costs.
I think it's any softwood that hasn't been kilndried (as the kiln drying process removes the phenols), and most cat litters don't specify or smell very pine-ish