When I ride it, I am usually alone (and female). I try to be "street smart" in whatever I do, and I find that particular section of trail to be a little too isolated for my taste, unless I know that a lot of people will be out on it.
I think that when I am on the Chateau trail, I am aware of the narrowness of the trail, and the encroachment of high vegetation - grasses and bushes. That means my lateral vision is somewhat impaired. I don't like the inability to anticipate what might be ahead that results.
I know from experience that there are areas on the trail where I have to slow to a crawl to get past the barriers, so I can't really get up too much speed on the trail. I also know that it is really hard to make a turn OFF the trail onto one of the side streets due to the presence of barriers, the absence of curb cuts, and the lack of warning as to where the streets ARE due to the high overgrowth. So, if I do get spooked (and I did once, very innocently), I feel like I have no place to go to escape, other than the river.
Once on side streets, I am likely to have to travel close to a mile to find any sort of assistance, should I need it (unless I were to flag down a motorist passing on Beaver Avenue, in which case I would only be about three blocks from assistance).
Note that these are all based on my PERCEPTION of safety, not any actual threats or issues on the trail per se. So, the trail might be perfectly safe for you to use at any time.
In this case, I recommended against the use of the Chateau Trail for his thread specifically because the original poster wanted a well lit area to suit his wife's needs. I don't think this trail is as well lit as the ET or the North Shore Trail, which benefit (a little bit at least) from the streetlights on adjacent River Avenue or Parkway/Second Avenue).
Finally, I think I am willing to believe that the Chateau Trail is less safe than other trails because I find it boring, and I ride it less often than I ride other trails. So, I have little evidence to the contrary.