How do I identify the remote db agent name to use in create_database_destination on Oracle 11gR2?
Scheduler agent is part of database Oracle Home. Anyway must be manually deployed; there is no way to use the database as agent. I think that the documentation is misleading on this case. To help you I will write steps to be performed for agent configuration. I suppose that on the central database you have already enabled HTTP port (etc.).
On the remote database (the one where agent have to be configure):

cd $ORACLE_HOME\bin
extjobo -createagentzip execution_agent.zip


Unzip the file into a directory under the $ORACLE_HOME\scheduler.

cd $ORACLE_HOME\scheduler
unzip execution_agent.zip


Modify the file named schagent.conf located in the $ORACLE_HOME\scheduler\execution_agent directory setting the Scheduler Agent port number to listen for connections. (the one you should have already set with dbms_xdb.sethttpport() )

PORT=&lt;schagent_port&gt;


You have to run the root.sh to fix the uid. (You can follow the README file in the execution_agent directory and run the root.sh). NOTE Verify a directory named /wallet exists under /execution_agent/data before running root.sh. If not create them manually and then run root.sh. 

Register the database with.

set ORACLE_SID=&lt;your sid&gt;
cd $ORACLE_HOME\scheduler\execution_agent\bin
schagent -registerdatabase &lt;db_host&gt; &lt;db_http_port&gt;


You will be asked to input the registration password. Last start manually the agent:

schagent -start


These steps will install and configure the agent. Now you can create credentials on the central database and create the database destination. Database destination can exists along with a remote agent destination.