I think everyone has a different opinion on that. I feel that treats fed too often become so normal they're not really much more special than anything in the mix itself and they could just unbalance the diet so I don't feed treats daily and vary what treats I do give. Others give mealworms daily yet regard them as still a treat and personally I don't really get that - if we fed a treat daily our pets'd see it more often than some of the ingredients in their proper mix. I prefer my hams to get as balanced a diet as possible so treats really are extras that they get less often instead
That said - our mix contains loads that our pets love so a few things many would use as treats are just part of the regular diet most of the time (like mealworms, they're in our mix but we give a few extras once in a while as treats too because the hams really enjoy them). Most of our treats aren't in the food mix though (like linseed, dari, cat kibble, coconut, eggbiscuit...)