This example shows that you can use Scala in Amazon Kinesis Data Analytics for Java Application. It is a staight-forward translation from Amazon example at https://docs.aws.amazon.com/kinesisanalytics/latest/java/get-started-exercise.html.
I translated StreamingJob.java to StreamingJob.scala and modified the Maven build file pom.xml to build the Scala project.
The build output is target/scala-getting-started-1.0.jar.