You need to inform Hive of your intent to use that JAR file. To do this from Tableau, use the Initial SQL settings in the connection dialog to create a line like this:
add JAR /usr/lib/hive/lib/hive-contrib-0.7.1-cdh3u1.jar;
You can find more details in the following Knowledge Base article: http://kb.tableausoftware.com/articles/knowledgebase/cloudera-hadoop-hive-extra-capabilities
I hope this helps,
where is the folder /usr/lib/hive/lib located?
Is it on the machine where Tableau desktop is installed, on HDFS or on where the hive binaries are located in hadoop?