I am not certain but I see that the D2 is part of the Dusit Hotels Group and they have had a joiner's fee policy for some years now.
There is a review of this hotel in SPICE Magazine which is gay but they don't mention joiners. You could e-mail the hotel as enquire what their policy and fee is for joiners. In my experience replies are few. Perhaps, as hotels in Chiang Mai are hurting with very low occupancies they may.
http://www.spicemag.net/hotelreview.php