So far in my reading, the TV out adapter has been offered as a (pre release) option for the GSM Diamond just not released from HTC them selves yet (it was probably pulled due to the fact they wanted to give the pro an exclusive option). what this means is it is compatible just not with the stock rom. (there is where my nice Raphael dump comes in) i did alot of surfing yesterday and foudnd a few places that talked about this adapter with the Touch Diamond and its future availability and functionality. the adapter carried the same part name as the Rapahel one
Youtube video on the diamon on tv out :P
http://www.youtube.com/watch?v=YTd3SUPSJsM