Yes you can see market depth. A ruby gem is basically a library to help get data from bitcoin.de written in ruby
I'm rather looking for public API of market depth for bitcoin.de. Not yet available?
Our API involves market depth. You can register for a API-Login. If you verify your account with your mobile phone our stuff will send you the keys for the API. Sometimes this needs some days. If you have trouble with it feel free to ask me again.
kind regards
Christoph Bergmann