Second question first: Yes! You can use any of the Java libraries. Interoperability is definitely a strength. Once you try using the Scala collections library, you probably won't
want to use the Java collections, but it's all there. Many of my Scala projects have long lists of Java library dependencies (Joda time, for example). Importing a Java class or interface is really no different than importing a Scala class or trait, except of course Scala-specific features aren't available. It's also quite easy to create Scala objects that extend or implement Java classes and interfaces.
The answer to your first question is also yes, Java skills are transferable to Scala. That's a double-edged sword. You can make your Scala feel and behave like it's just a syntacticly different version of Java, and apply the same OO design principles as you would in a Java environment. It'll work fine, and your productivity in Scala will quickly become on-par with your productivity in Java. The other answer to your first question is no, Java skills are not helpful (and in some ways detrimental) to using Scala as a
functional language. It's a very different mindset, but it's also where some of the bigger gains in productivity are to be found. The temptation to do something the Java way can be hard to overcome and think through a functional solution. I highly recommend taking
Martin Odersky's class and really pushing yourself to develop functional skills to complement your OO skills.
Edit: typo and implement java
interfaces rather than objects