Either the GM is new, doesn't understand the situation, or isn't fully aware of the ToS, because trading gil for housing is in no way a violation of the ToS. There isn't any actual RMT going on here -- just players exchanging gil for a service (the right to relinquishment).
I understand that gil isn't even being exchanged in this scenario, but the above still rests. The only thing that might flag your account is exchanging large quantities of gil, which might place you under review.
However, what is debatable is if they will investigate and do something in case there is a scam or the transaction goes awry.
If you want clarification, I'd not only e-mail support but also put this up on the official forums. They might take it down due to the GM's name being visible, so that should be blurred. Hopefully that will give a better response as to whether this GM's opinion overrides the actual Terms of Service.
I understand that gil isn't even being exchanged in this scenario, but the above still rests. The only thing that might flag your account is exchanging large quantities of gil, which might place you under review.
However, what is debatable is if they will investigate and do something in case there is a scam or the transaction goes awry.
If you want clarification, I'd not only e-mail support but also put this up on the official forums. They might take it down due to the GM's name being visible, so that should be blurred. Hopefully that will give a better response as to whether this GM's opinion overrides the actual Terms of Service.