Cockroaches and some diseases have been linked because these wee buggers do crawl around "stuff" that is known to harbor disease pathogens and where cockroaches are prevelant Asthmatics seem to have more problems, in the home. Since cockroaches are common outside in Forida and other warmer areas of the world they may be a normal part of the environment, but are extremely difficult to control out there whereas in the house control is, relatively, easy. People have been trying to eliminate Cockroaches for many years with very little success so maybe they do have a place in the world.
Since Cockroaches, outside, are not a really big problem I would not spend a lot of time, energy, and money on some eradication plan that probably will not work anyway.

I am not trying to eradicate the small roaches in my back yard, I am just unsure if they are helpful or harmful to my yard. Should I be concerned if I have a high number of them? I know my soil is in terrible shape. I have been digging up several areas of my yard to install native plant flower beds and I have yet to see one earthworm.

Cockroaches have survived for eons because they have learned to eat most anything, so they could be aiding in digesting what ever organic matter is in your yard. In the yard they probably are not really harmful as they could be in your house.

I don't have them in my house. I don't mind them in the yard. I was just curious if I should be concerned about them effecting the health of my grass.

In my opinion, they are not a problem outdoors. In fact, they might be of some value. If you are fully organic and don't use insecticide, herbicide, or synthetic fertilizers, then you should have ample lizards, birds, geckos, and toads to control the population of all insects.

ok ok, roaches Are bad, PERIOD. not so much eco system bad, but just so damn annoying and contaminates everything. if you are growing tomatoes and potatoes, (mmm)...then get rid of them i.e (ants).
Now they are good as far as circle of life, they attract other insecests that prey on them, some of these inscests may be of TRUE value to your lovely garden *might i add.
hope to help,
Dre'
S.C

If you are an organic gardener then you need to rid yourself of the "every insect is bad and needs to be eliminated" mindset expressed above. Unless the particular insect is creating a problem that is too big for you to live with there is no good reason to do "something" to get rid of them since they are part of the world we live in and provide a food source for something that is probably beneficial.
A very few insects, Tse Tse fly, malarial mosquito, etc. come to mind, should be controlled, but other then those very few need a braod specturm poison sprayed around.