Peter Thiel happens to be a sponsor of MIRI, which makes it seem more credible when people talk about "his" ideas on a website associated with MIRI.

That's a valid concern indeed.

even if all LW readers would understand what this is all about (creating a place to post mostly NRx-y ideas, while pretending to talk about Peter Thiel), a random visitor would see Peter Thiel in the title and the ideas below

Random visitors who are prone to poor reasoning in all sorts of creative ways could stumble across almost anything and draw wildly inaccurate conclusions about what they read. I don't see any reasons that the opinions of such persons should be much of a threat to anyone but themselves.