The backend database is MySQL and the database name is the same as your application name (using getenv('OPENSHIFT_APP_NAME')). You can name your application whatever you want. However, the name of the database will always match the application so you might have to update .openshift/action_hooks/build.
Note: When you upload plugins and themes, they'll get put into your OpenShift data directory on the gear ($OPENSHIFT_DATA_DIR). If you'd like to check these into source control, download the plugins and themes directories and then check them directly into php/wp-content/themes, php/wp-content/plugins.
GIT_ROOT/.openshift/action_hooks/deploy: This script is executed with every 'git push'. By default, this script will create the database tables that this example uses.
If you need to modify the schema, you could create a file
GIT_ROOT/.openshift/action_hooks/alter.sql and then use
GIT_ROOT/.openshift/action_hooks/deploy to execute that script (make sure to
back up your application + database w/ 'rhc app snapshot save' first :) )
Consult the WordPress documentation for best practices regarding securing your wordpress installation. OpenShift automatically generates unique secret keys for your deployment into wp-config.php, but you may feel more comfortable following the WordPress documentation directly.