this, i think is a bad thing, a very bad thing. this is because it operates on the principle that your research should be entirely novel, and really, it hardly ever it, the best part of the dissertation is the building on the prior knowledges, not that this is what they really mean, but if you go there and look before you choose your topic, you will feel entirely wrong. a dissertation should be constructed from either your positions and passions or from the situated necessities of your department and committee. You should not feel that if someone else is doing a similar things that this impinges on your research at all, even if you have contradictory theses, that's even better. I mean this is about knowledge, so the project you understake has to be understood as furthering knowledge, if it compliments, contradicts, parallels, etc. that accomplishes the goal.