When your job is executed, the "controller" logfile contains the actually executed commandline. This could look something like:
2014-06-02T15:37:47.863Z INFO Fetching jar file.
2014-06-02T15:37:54.943Z INFO Working dir /mnt/var/lib/hadoop/steps/13
2014-06-02T15:37:54.944Z INFO Executing /usr/java/latest/bin/java -cp /home/hadoop/conf:/usr/java/latest/lib/tools.jar:/home/hadoop:/home/hadoop/hadoop-tools.jar:/home/hadoop/hadoop-tools-1.0.3.jar:/home/hadoop/hadoop-core-1.0.3.jar:/home/hadoop/hadoop-core.jar:/home/hadoop/lib/*:/home/hadoop/lib/jetty-ext/* -Xmx1000m -Dhadoop.log.dir=/mnt/var/log/hadoop/steps/13 -Dhadoop.log.file=syslog -Dhadoop.home.dir=/home/hadoop -Dhadoop.id.str=hadoop -Dhadoop.root.logger=INFO,DRFA -Djava.io.tmpdir=/mnt/var/lib/hadoop/steps/13/tmp -Djava.library.path=/home/hadoop/native/Linux-amd64-64 org.apache.hadoop.util.RunJar <YOUR_JAR> <YOUR_ARGS>
The log is located on the master node in /mnt/var/lib/hadoop/steps/ - it´s easily accessible when you SSH into the master node (requires specifying a key pair when creating the cluster).
I´ve never really worked with what´s in HADOOP_CLASSPATH, but if you define a bootstrap action to just copy your libraries into /home/hadoop/lib, that should solve the issue.