There is a log4j rpm for tomcat6. But for tomcat5 to use log4j, user needs to manually copy the log4j library and configuration file. It makes sense for an rpm installation to have user install an rpm to get some functionality. I believe that asking the user to deal anyhow with non-configuration files is against the idea of rpm installation and removes rpm benefits user expect.
So to me it seems most appropriate to have a common log4j rpm. Then tomcat5 and tomcat6 specific RPMs that create appropriate links to the log4j library and configuration file. IMHO user can only be asked to edit configuration files or a functionality cannot be `supported'.