With Jrebel for Eclipse installed, normally a Server's configuration tab in eclipse will have a section for Jrebel which includes an option to "Enable Jrebel agent." A screenshot of a server's configuration tab can be seen below with the Jrebel section in it (liferay-6.1-jrebel-working-correctly.png). This works for Liferay Portal 6.0 and 6.1 servers created with Liferay IDE.
However when a Liferay Portal 6.2 Server is created via Liferay IDE in eclipse, there is no Jrebel section in the configuration tab. The server configuration page missing the Jrebel section can be seen in the screenshot below (liferay-6.2-jrebel-section-missing.png). If this page is mising, Jrebel cannot be enabled for a server from within eclipse.