[Ria P]

My dwarf Clarissa does that sometimes and has naps on the surface and i've heard of other hamsters doing the same so i don't think its anything to worry about.

As for plastic tubes, is it just one tube to run through? Plastic tubes can be a problem when a hamster sleeps, nests, pees or hoards in them because they are hard to keep clean and condensation and mould can cause bacteria that can lead to health problems.
Hamsters love tubes though but cardboard, cork, wicker etc tunnels are far better than plastic. I use a long bendy plastic tube in the out of cage time play area and they all love running through it.

What kind of cage does Oreo live in? I find that a cage like the Hamster Heaven with all or most of the plastic removed works really well for a dwarf because the large front door makes interacting easy.

Itching and excessive grooming can be a sign of nervousness and sometimes the hamster grows out of it as they become more settled.
It can also be a sign of diabetes which was the case with one of my dwarfs who was diabetic and scratched a lot but never to the point of making his skin sore.
I would have taken him to a vet if his skin would have been red or inflamed.
It can of course indicate other issues like mites but i wouldn't want to speculate on the reason your Oreo itches. (Personally i would never have one of my hamsters treated for mites without a definite skin scrape diagnosis).

Also, what one person classes as excessive itching may be seen as normal grooming by another.
Sorry i can't be more helpful or specific on that subject.