I will first distinguish between the commercial use of the theme with in-line content above and the current use of the 173 page. The mere presence of advertisements does not make a work commercial, as I will explain below, whereas the vendor's use of the theme solely to move ads counts as a commercial use.
I will first quote from our correspondence with Mr. Kato to set the ground.
I will reluctantly permit this secondary use of the image of “ Untitled 2004” as SCP173 unless SCP foundation use it for commercial reasons, because there is a situation that many people have recognized SCP173.
Emphasis mine.
For lack of other instruction, a valid interpretation of the above segment given the context is specifically granting the SCP Wiki the right to use Untitled 2004 (when expressed as SCP-173) under CC-BY-NC-SA. But let's take a look at what the CC-BY-NC-SA license actually says:
NonCommercial — You may not use the material for commercial purposes.
And then, on a hover-link on that page, but also equivalently defined here.
“NonCommercial means not primarily intended for or directed towards commercial advantage or monetary compensation.”
Is the SCP-173 image, or to make the question easier, the entire page, "primarily intended for/directed towards commercial advantage/monetary compensation"? Considering the fact that neither staff nor Moto42 have seen one thin dime as a result of that page (or, really, any page), as well as the fact that the work is entirely separate from the ads (which are, indeed, not even visible to a great many visitors as they are disabled upon log-in), it can be definitively stated that the wiki's use of the image does not count as commercial for the purposes of CC-BY-SA 3.0, even if ads are displayed alongside it.
What about Wikidot? They, admittedly, must profit from the ads (I have no actual proof, but it is a matter of common sense). Indeed, they are very likely hosting a wikifarm in order to make money, I certainly doubt it is a passion project on their part. So is their use, at one layer of abstraction through our use, commercial?
The foremost argument is that we are not Wikidot's keepers. It is a compelling one, and certainly an accurate one, but it also dances around the answer: that in a legal sense, Wikidot's "use" of it does not count as use at all. Essentially, as far as the image on this page is concerned, the buck stops with the SCP Wiki.
Wikidot is not "using" the Untitled 2004 image from a legal standpoint. It did not upload it, it merely hosts it while remaining agnostic about the copyright status of it and all other images it hosts. Wikidot is covered under the Digital Millennium Copyright Act Article 512(c) safe harbor provision. It is completely non-liable for our use of the image (with the exception covered in the footnote above), which is non-commercial, while their exemption from liability means their use and profiting from advertisements does not effect the licensing status of Untitled 2004 in any way.