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What are the issues and incompatibilities between RTC 5.0.2 and RAD 8.0.4?

I've been told by IBM that RAD 8.0.4 is not compatible with RTC 5.0.2
I realize RAD 8.X is out of support.
I have a dev team that is working in RAD 8 and cannot migrate off of RAD 8 at this time. I Am trying to schedule an upgrade to 5.0.2.
In my testing I was able to install the RAD 8.0.4 and RTC 5.0.2 repositories together through IM 1.8.2/3 and while I got a warning of incompatible bundles, they installed and I was able to connect to a repository, make a change, see the change in pending changes, check in deliver, and create an associated workitem.
This is our base level test.
I'm hesitant to offer this is a temporary solution to this dev team without know what the risk is.
Does anyone know what the potential incompatibilities are?
2 answers

If you use an Eclipse 3.6.x base, chances are it just works. But you need to be aware of any conflicting packages in the shared environment. For example, the RTC installation is known to replace some packages of newer version silently (IIRC that's JDT and the result was the loss of Java 8 support).
Once again, you have to do your own testing for such combination.