A hatch, according to the documentation I have read, is a recurring pattern of lines. The size of the pattern to be recreated can be increased so that there is only 1 or 2 repetitions of the pattern, but it will not be truly random.
What if rather than using a hatch pattern, you used an mtext object then used a random number generator in a lisp to fill it in.
If you needed it to be an unusual shape, then you could create it in modelspace, then apply the view in paperspace with a polygon viewport.
