That's because the call to addToolsJarToClasspath(classpath) is missing in the WebLogic 8.x implementaiton (as it's done for Resin, Tomcat and Orion).
I suggest modifying AbstractContainer to systematically add tools.jar in the CP for all containers (and thus remove the addToolsJarToClasspath(classpath) calls in Resin, Tomat and Orion
I also suggest adding a JSP file to our functional test suite as tools.jar is usually needed to compile the JSP files. This will uncover the issue. Do this before implementing the solution so that we're sure to be reproducing the problem.