Bleach spots, unfortunately, often will not redye.. and even when they do, still won't dye evenly. If you do try.. use 3-4 times the usual amount of dye, stir constantly. .and I do mean the whole danged time .. rinse 'til clear.

Blacks home-dyed.. I've yet to see anyone get a home-dyed black to be as black black as industrially dyed black.

Have you thought about intentionally bleaching other areas.. to get an all over spattered look? That could be kinda col.
Browse thru the dyeing tips & tricks .. there's a lot of good info in there.. or go to dharma trading.. www.dharmatrading.com I know somewhere on that site they talk about black dye.

Many years back, I had black jeans for work that I got bleach on. To help the dye take better, I colored in the spots with black fabric marker before dying them. It didn't last long before the bleach spot came through - maybe a handful of washes - but it seemed to help somewhat. I don't know how different materials re-act to that method, but it might be worth a try. I did it that way because that is what someone recomended to me. It was a brand new pair of jeans, so I was willing to try anything. I ended up just coloring in the spots each time I wore them after the bleach started showing through again. It was just a couple of quater sized spots near the front pocket area, so it wasn't a big deal to color them. Hopefully there is something better out there for this problem now.

Also, if they're cotton, you should probably use Procion dyes (available from Dharma or most craft/fiberarts stores) instead of direct dyes like Rit or Tintex. Procion dyes are richer and more colorfast, don't fade much, but are a bit more involved in terms of the dye process. Definitely use a higher concentration of dye powder in the mix.