It would be a great way of learning Scala.
I was actually evaluating different Scala frameworks and stumbled upon this project as well as another neat one: https://github.com/ornicar/lila
In the case of GitBucket the most important advantage is its easy installation, especially when compared to the more well known GitLab (that I never dared install after reading through the installation instructions).
For me it is :). I started to learn Scala after finding this nice project. Since it was so easy to install it (just copied the WAR file in a running Tomcat) it made me curious enough to give Scala a try and also to buy the Scalatra book too :).