IIRC, they were mentioned in "The Shadow Within" (just bought two, one for a gift; BTW, GREAT cover), and the Technomage Trilogy.
Kribu, the thing is, How widespread is that knowledge, and would somebody be able to connect the race name with a physical appearance? I think you're right about them being the ones to operate on Londo. I also think they're the ones...
Spoiler for "The Shadow Within"
<font color="yellow"> Beginning of Spoilers Space! Highlight lines below to read. </font color>
...Anna sees operating on the Icarus crewmates, getting them ready to be Shadow Ship CPUs.
<font color="yellow"> End of Spoiler Space. </font color>