Unless you really want to use Log4J as the logging back end (which, in 2.0, generally won't be necessary as now embed LogBack), you don't need to add the log4j bundle to the repo. Instead you can just use the Log4J to SLF4J bridge that ships with dm Server.
In your bundle, just import the Log4J packages and proceed as normal. If you app is a standalone bundle, it will generate log output to serviceability/logs/log.log. If your bundle is in a scope, i.e. it's referenced by a scoped plan, or included in a par file, it will generate log output to serviceability/logs/<scope-name>/log.log.