Dermastid beetles can fly, and in doing so may pick up illness and disease from outside your colony, when they return your colony becomes I'll and dies or survives the illness and becomes a vector for that illness to get into your gecko.
Springtails of any sort I deal with will not thrive in a properly cared for roach colony. They might do fine in a tropical enclosure housing Madagascar hissers but when humidity falls below the point where condensation forms they die.
Cleaning by hand is not hard and keeps sanitary conditions for your feeders.
Breeding your own feeders is only cost effective if you breed healthy feeders, a single visit to a vet to get rid of some nasty internal parasites or illness can wipe out savings in a hurry.
Depending on what you are feeding your colony will determine what if any additional insects could live in with a roach colony, for example, the dermastids you mentioned require a dietary source of cholesterol, without it they will die off due to lack of it. This takes a while, they can source it from dead dermastid beetles and make it a few generations until the quantity available is so small that no larva reach maturity. A 100% vegan diet fed to the roaches can help eliminate them, conversely a diets containing cholesterol will support them, via the cholesterol voided in waste or by consuming any roaches that die in your colony that have consumed cholesterol.
Regardless, if you feed your colony waste will be produced, it can not be avoided. If your adding other insects even if they are consuming the waste, they in turn are going to produce their own waste. What you end up with is a colony of feeders infested with a colony of bugs that are not suitable for use as feeders (mildly debate able but I'm not going there right now).
You would do best to avoid allowing your colony from having feeder roach losses due to illness, disease, old age, or injury, not even mentioning dehydration or starvation.
This is done by properly rotating adults as breeders, once they are past their prime breeding age feed them off.
This reduces the number of mouths you are feeding and waste that is ultimately produced.
Maurice Pudlo