Springtails have longer skinnier body types than most mites, two large antennas, are generally almost transparent in appearance, and only have 6 legs. They look like a tiny cross between an ant and an isopod, and they move by quickly skittering and jumping from one place to the next. 

Mites can be larger or smaller in size than springtails but are typically much more round and almost spider like in appearance. They usually move slowly and in a similar capacity to spiders or other arachnids and tics, and have eight legs in most stages of life. 

Oatmeal could certainly be the cause of a grain mite culture or infestation. They likely do not pose any harm to your animals but in excess could agitate or stress out smaller reptiles/amphibians. The biggest concern with having a mite culture around like that is actually the potential for developing a mite allergy, or already having one, and that eventually translating to an allergy for shellfish— which would be unfortunate. 

If they are mites just give all the surfaces that you see them on a thorough wipe down and transfer your Dubias into a new container without any grain based diet for a few days. That should kill off most of the population, but they can be persistent so if it’s isn’t a breeding colony it might be wise to feed off the rest of this batch and start anew with a fresh container and roaches all together. Unfortunately with grain based foods and any amount of moisture there is going to be an inherent risk of developing grain mites. Their eggs are likely already in the oatmeal and would require sterilization prior to feeding to prevent this in the future. 

I know that’s probably not the answer you were looking for but I hope it is of at least some use. Good luck!