Question does XFCE use the same GTK mottle, whatever that means, as Gnome and if so will it run Orca?
According to the following message, Xfce 4.4 does, and should run Orca.
It’s worth looking into.
According to the following link, Orca did give the welcoming message under XFCE but nothing further.
The following says that orca will work with Firefox, while in Xfce, but Orca is terminated when Firefox is closed.
From the message:
By default Xfce does not set the required environment variable to make gtk use the accessibility backend (atk -> gail), i've created a bug  for that, because that is indeed quite important. To enable this in the toolkit you can do 2 things: 1) Create a .gtkrc-2.0 file in your home-directory and add the line: gtk-modules="gail:atk-bridge" 2) Export a environment variable GTK_MODULES=gail:atk-bridge
An answering message suggests that at-spi needs to be installed at startup It also suggests using Lxde.