Yes, they need shoe trees. Shoe trees aren't just for helping to minimize creases. Minimizing creases is an incidental effect of a healthier shoe due to the fact that the shoe isn't able to bow upwards when it is drying after being worn. Moisture, especially salty moisture (think sweat), is detrimental to long term leather health, so absorbing the moisture into the cedar is best for the leather. This is actually even more true on an unlined shoe, where the same leather touching your feet on the inside is also the leather that is taking a beating on the outside.