If you set JENKINS_ENABLE_ACCESS_LOG="yes" in /etc/default/jenkins, the startup script in /etc/init.d/jenkins appends -accessLoggerClassName... to DAEMON_ARGS.  This is incorrect and causes jenkins startup to fail with the error

Dec 12 10:50:43 dtg-jenkins jenkins[28926]: /usr/bin/daemon: unrecognized option '--accessLoggerClassName=winstone.accesslog.SimpleA
Dec 12 10:50:43 dtg-jenkins jenkins[28926]: usage: daemon [options] [--] [cmd arg...]
Dec 12 10:50:43 dtg-jenkins jenkins[28926]: options:
Dec 12 10:50:43 dtg-jenkins jenkins[28926]: -h, --help - Print a help message then exit
...

Changing the line in /etc/init.d/jenkins to 

     JENKINS_ARGS="$JENKINS_ARGS --accessLoggerClassName=winstone.accesslog.SimpleAccessLogger --simpleAccessLogger.format=combined --simpleAccessLogger.file=/var/log/$NAME/access_log"

makes jenkins start correctly and the access log appear correctly in /var/log/jenkins/access_log