Though the article speciefied above does not refer to RDZ, it does say that Rational Developer for Power 8.0 will work. Based on this and your comments I infer that RDz will also.
If you want to use the RTC-RDz integration feature with RTC 4.0, you need RDz 8.5. Here is a nice blog post by Rosa Naranjo outlining your options: http://rhnaranjo.wordpress.com/2012/09/21/rdz-rtc-compatibility/
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