Load testing is not done within Eclipse but by running the script mastercontroller.cmd in Windows, and mastercontroller.sh in Unix respectively. But load testing requires that all of your Java source files were compiled to Java Bytecode - either by Eclipse, any other IDE or a build tool like ANT or Maven.
Once your classes are compiled, you'll need to make sure that
mastercontroller.properties is set up correctly as documented here. Also, don't forget to adjust project.properties which specifies the load test scenario mappings and the name of your load test settings file (test.properties per default). This file contains all settings for your test run: the scenarios that participate in the run as well as their load profile.
So, in short, yes this the proper way of configuring load testing in XLT. Further configuration steps are necessary in case you want to run your load test from remote machines.