Hello Arun,
You are right, starting from SonarLint for Eclipse 7.0 the Eclipse IDE host needs to run with Java 11 for the plugin to work.
I don’t know much about Rational Developer for I Series, isn’t there a newer version that supports Java 11 ? As a fallback you can still continue using SonarLint for Eclipse 6.2. You can install it through our update site, see instructions here. As it’s not the latest version you will need to untick the “Show only the latest versions of available software” option in the Install dialog. Also please note that we might drop this older version from our update site in the future.
Hope this helped