...

  <property>
    <name>general.vfs.cache.dir</name>
    <value>/opt/accumulo/tmp/</value>
  </property>

You can verify this in the shell:

root@local> config
...
default    | general.vfs.cache.dir .................................. | /tmp/accumulo-vfs-cache-hdfs
site       |    @override ........................................... | /opt/accumulo/tmp/accumulo-vfs-cache
...

Namespaces

Namespaces provide logical groupings of tables as well as a great way to configure GeoMesa Accumulo's classpath. When coupled with properly configured VFS classpath contexts, it is easy to upgrade your system between GeoMesa versions or support multiple geomesa versions on the same cluster. It is recommended that namespaces should be named for applications and NOT for geomesa versions since this makes upgrading them and running multiple applications/versions on the same cluster confusing.

...