As SecretlyDying said robos aren't one of the species prone to diabetes so you don't need to worry about that although it's still a good thing to avoid all sugary treats as they are generally unhealthy for any animal.
Mealworms make a great treat in moderation, they are a good protein supplement but also high in fat so not too many!
There are a variety of seeds that you can give, sunflower (in the shell), pumpkin, flax & hemp seeds are all healthy, millet is generally enjoyed if you give the sprays (often sold for birds) monkey nuts are also good as an occasional treat, very tiny bits of other nuts can be given too.
If you don't give them already fresh veg, just small amounts daily are an important supplement to the diet & a real treat for hams too.
I would use a dwarf specific mix, the pets at home muesli isn't ideal, the Burgess dwarf hamster harvest is quite good but does lack variety so they can get a bit bored with it, the B
unny dream mix from Zooplus has a lot more variety but is a little low in protein but if you give mealworms you'll easily make that up.
I really wouldn't recommend the JR farms mix.