After comparing label after label, I've FINALLY determined that you CAN use poultry feed for rodents. You just need to use caution when choosing exactly which poultry feed to use. Do NOT use egg-layer feed, unless gutloading is necessary for calcium deficient animals, and then you should only use it for 2-3 days before feeding the rodent to the calcium deficient herp.
A general purpose "raiser", "starter" or "grower" poultry feed fits the same rodents that would be fed on a Harlan diet. I would go for a 20-24% protein diet for a breeding colony. Also, when buying your poultry food, make sure you either get crumbles or pellets, NOT mash (powder). The pellets will be about the size of the alfalfa pellets in a lower quality rodent seed mix. The crumbles are generally very small, just crunched up pellets, generally a good size for very young rodents.
A downfall to the poultry feed would be that it isn't as hard as the blocks, and chew "toys" would be necessary to keep incisors worn down.
What was the point in taking all of this time to check the labels and do a bit of research on mouse/rat nutrient requirements? Well, first, Purina Mazuri and Harlan products are not always easily obtained, and second, in most circumstances, the poultry food is going to be MUCH cheaper than rodent foods. Rodent blocks in my area cost $1.05/lb, while proper poultry feeds purchased at Tractor Supply (Dumor brand) are about $.33/lb. If I were to take the time to drive to the Purina mill, I could probably get it for about $.20/lb. The poultry feed could cut your feeder bill in half, without sacrificing essential nutrients.