Hoping you have completed all the pre-requisites to run spark on Mesos, however please follow below if you haven't done yet.
http://spark.apache.org/docs/latest/running-on-mesos.html#connecting-spark-to-mesos
Regarding spark + Mesos and Tableau connection, I believe you need a SparkSql thrift server so that Tableau can directly connect to the thrift port. Morever you can start your thrift server like below.
$SPARK_HOME/sbin/start-thriftserver.sh --master mesos://host:port --deploy-mode cluster --executor-memory 5G
Note: You also need spark ODBC driver at Tableau client side to connect to the Thrift server, you can download it from Here