I'd be very curious to see the actual "advertisement(s)" that sparked this thread, to see how they are worded. Unless I missed it, I don't see a link to them.
Without knowing exactly how the promotion of this station rental is being done...
In general, I don't see a problem with this under current FCC rules. Reasoning:
(1) Part 97 (in plain English) prohibits an individual being paid to operate an Amateur station, with a noted exception for specific bulletin & code practice stations. That does not seem to be the case here.
(2) Part 97 prohibits an Amateur station from selling advertising, transmitting music, or otherwise operating as a Commercial station. That does not seem to be the case here.
(3) Part 97 does NOT prohibit a station from being made available to another operator. It does not address (for or against) the means. Thus, it does not prohibit someone from renting their station (at cost or at a profit) to another amateur. And THAT does appear to be the case here.
If it is not prohibited, the legal implication is that it is allowed. It may be distasteful, and the requested rental fees might be high (for any of a multitude of reasons), but it does not appear to be legally prohibited under Part 97.
Now: I am not a lawyer. However, if this ever became a personal issue for me, and I needed to confirm with an attorney that my opinion appears to be correct, I'm fortunate enough that my attorney is a ham. So if there is any doubt, I would politely suggest that the matter should be discussed with one's local Volunteer Counsel for a definitive answer.