This may be a silly question, but is there a problem with having a dishwasher sit directly on a wood subfloor (is this done often)? Or should there be some type of flooring over the subfloor? I guess I was thinking that something might be better than nothing to protect the subfloor should a leak develop, but it would be easier to not add additional flooring.
Your dishwasher and all appliances for that matter are sized to sit directly on the finished floor. If it sits on the subfloor it will sit too low under the countertop. Furthermore, it would be difficult to pull it out over the lip of the finished floor if you ever wanted to replace or repair it.