Danny,
I don't see a real problem with much of any species of wood as long as it can be: 1. bent to the desired form 2. isn't oily so as to cause epoxy problems and 3. is light (if that is what you so desire). One of most commonly used core materials in high performance composite construction is cork. Not suitable for much in so far as structural properties alone, but serves the above purpose quite well. The core material properties are important and can definately add to overall "strength", but that is not what generally accounts for it. The glass sheathing and distance apart (core thickness) is what makes monocoque hull construction work.