The Dead Stars Nebula, though it may be in some respects similar to the one surrounding Asphodel, does not mask emissions as much as theirs upon reading their NS. It is fully possible to see the extent of civilization within the Dead Stars, though what would be found from scans would be a large region of very inhospitable space with few planets inhabited by organic life. I'll also throw my own hat in the ring of "FTL probably won't work there" by siding with the creative decision behind Asphodel's nebula and saying that the Synch's own drives probably wouldn't be able to achieve a lock with the system. This is more because the Synch's systems relies heavily on achieving a point of syzygy with the opposing planet/star, and their dark nebula would make things very difficult.