Yes, it is fine to feed your feeders dog food. I choose dog food made from organic products or ones that are very low in fat. I also use fruits, veggies and vitamin/calcium powder to feed my feeders as well. (mealworms and dubia roaches). Just like your geckos, variety is the best option.
I would actually avoid dog and especially cat food. In other reptiles, like chameleons, feeders consistently gutloaded with animal protein will lead to gout. These foods tend to be high in fat and preformed vitamin A as well, which is easy to overdo in reptiles. For anyone who isn't familiar with gout in reptiles, it is a build up of uric acid in the bloodstream that typically ends up impairing renal function (kidneys), causes damage to the joints, etc. And the problem with roaches is that they build up uric acid and do not excrete it like other invertebrates, which means that if you've been feeding your roaches dog food for weeks by the time you feed them off they are just choked full of uric acid.
If you are only building up a colony it's ok to provide small amounts of animal protein (although not necessary) but when feeding them off it is way safer to stick to a veggie/fruit gutload and/or a commercial gutload with moderately low levels of protein.
Yup I'd avoid dog/cat food, they usually contain too high of a protein content and as said above, they lead to uric acid build up in feeders such as dubia roaches. See this article from Allen Repashy for details: