yes what you feed the rodents can effect how nutritious they are for the snake. I would suggest that you get a bag of lab block like this
http://www.reptilebasics.com/harlan2018
Dog food in general really shouldn't be fed to rodents (heck most shouldn't even be fed to dogs in my opinion...) rodents fed dog food tend to have all sorts of health problems.I havent heard anything on the gut loading thing but I have heard that there are things you could feed the rats that could be harmful to snakes but I am not positive as to the truth behind some of the claims. I have heard things with dies in them like some dog foods are not good for snakes and then I have also heard that some seedy foods that the rats eat can be harmful to the snakes. Not sure if they are true but I stay away from things that have this just to be safe...