Hadoop on Mesos fails with "Could not find or load main class org.apache.hadoop.mapred.MesosExecutor"
I found the problem. bin/hadoop of the downloaded Hadoop distribution attempts to find its location by running which $0. However, that will find a current Hadoop installation if one exists (i.e. /usr/lib/hadoop), and will load the jars under that installation's lib directory instead of the downloaded one's lib directory.
I had to modify bin/hadoop of the downloaded distribution to find its own location with dirname $0 instead of which $0.