Unfortunately, this post is over eight years old and that often means folks have moved on to other fun items and don't check the forum.
But then there is never a bad time to talk about what wood and our tanks do, so why not?
My thinking on what is and is not safe fits with what one poster said and that it is the sap or moisture in the wood, rather than the rest which is mostly just cellulose. It is quite common to read about cedar being dangerous to use but my experience is that it works fine if TOTALLY dry.
That is often a hard term to get across to folks who don't deal with wood much as totally dry doesn't mean the same as just feeling of it and not finding it wet or damp. Wood workers use the terms green or wet in a pretty different way than we do for most things, so dry means a lot different to them.
I also feel our different water is also a factor in what we can use without trouble. I have mostly lived in areas where the water is very hard and alkaline so it has tons of buffering and that keeps anything I put in my tanks from moving the PH in any real amount.
So part of my use of Cedar in tanks may depend on water which will not let any small amount of moisture change things due to the high buffering.
I treat new things in the tank very much like going swimming in a new place. I wade in carefully until I see what happens, rather than diving in head first!!
Try it and see how it goes---but carefully? Possibly why they sell feeder minnows in fish shops?