Rhaane did not invent the research productivity effect, it was already part of Factorio but not accessible by vanilla gameplay, this mod just made it accessible. I assume the developers used the same effect when developing their DLC. So you should get the sum of both research productivity technologies.
I can't test it with Space Age but the first version of this mod for Factorio 2.0 was released 13 days ago and it was downloaded 350 times since then. I think if there was a problem with the Space Age technology someone would have written about it already.
