I thought I should comment here as I may be the source of those comments on other forum.
There is a very good reason not to feed dog or cat food, or any other high protein food, to roaches. And yes, it will effect your reptiles by causing dehydration and unnecessary stress on the kidneys and liver. In their natural habitat roaches are used to a protein poor diet, they only need about 18% protein in their diets. As such, they have adapted in a very unusual, and impressive way. They are able to store amino acids in their blood and then synthesize these into proteins when needed. In the natural world, this means that on those rare occasions when they find a high protein food source, they ingest as much as possible and break it down into uric acid, which is stored in high amounts in their blood. Because it is rare in the wild, this is cyclical and they can handle these high amounts of uric acid for short periods of time.
However, if you are feeding this high protein source to your roaches regularly it can become problematic. The fact that most people are using dry food is what keeps the roaches from dying. If fed a constant wet, high protein dog or cat food you would find a lot more dead roaches, unable to deal with the consistently high levels of uric acid that would start to crystallize in their joints and organs.
What this means for your reptile is that you are feeding a high uric acid prey. Many reptiles already suffer from various levels of dehydration in captivity, so this high uric acid feeder prey can lead to further dehydration and related problems. Gout is caused by uric acid crystallizing in the joints and organs. Does that sound familiar yet? Even if not dehydrated, you are forcing your reptile to process higher than normal levels of uric acid, thus stressing their 'filter organs', the kidneys and liver. As there are already plenty of stressors for captive reptiles, the question becomes, why are you feeding your roaches dog or cat food?
Dog and cat foods, especially the cheap stuff most people give to roaches, are a horrible food source, even for dogs and cats! Roaches only require about 18% protein in their diet to grow healthily and reproduce. Any more than that and you are feeding a uric acid boosted prey. Look at most roach chows, the good ones are around 15-20% protein for a reason. They are also cheap and easily found online. If you aren't willing to take the time to feed them fresh foods, then at least be willing to feed them a healthy, cheap roach chow.