The pros and the cons:

Pro- "I have also had a hard time getting my rats to consistently eat lab blocks, so after reading a lot of dry dog food labels, I have decided to feed my rats a staple diet of Nutro's Natural Choice Lite dog food (pictured above left). At 14%, It has lower protein than most of the lab blocks readily available in stores*, and contains no dried corn; just lamb and rice. It also contains no preservatives, which is becoming a big issue with me. "

Con- if your rat only eats 5 pieces of dog food a day, she is not getting enough nutrtion. she would have to eat the same amount of food a dog eat in a day to benifit from the food. Some dog foods also have high levels of protein which is harmful to rats. 

All information was taken from:

Rats Rule Diet Page

Canadian Rat Mischeif 

As I said, feeding you rats dog food is a personal choice. If you choose to feed you rats dog food, remember to give lots of healthy treats as well. If you feed  only dog food, your rats will become vitamin and mineral deficiant.

The search for a good rat food is on!Check out these links:

www.labdiet.com

www.oxboyhay.com

These links have info on some of the most incredible animal foods.

i have found that hagen nutri-blocks are great. its advertised as a rat, mouse, hamster and gerbil diet but its way better than dog food or seeds. Harlan Teklad is also a good rat diet.