His tank set up looks lovely. I suspect his change in behaviour is after a few changes to the cage make him a bit nervy. He will adjust soon and become active again, but it might be an idea to hold back on taming until he does.
They do have different personalities and can be tamed, but it takes more effort than for a Syrian I think. Meanwhile he is familiarising with your voice and scent. I also thought Nugget didn't take nesting paper but he did - he just didn't take very much - they are so tiny.
The biggest problem I had was actually getting Nugget out of the cage for taming and sadly I never did get to tame him as he was so terrified. It was only when he got older it was slightly easier to get him out and he would walk into something.
So getting him familiar with your hand/eating from your hand would be a good start as then he might walk into something with food in. If it looks like he is never going to take things from your hand then try putting a mug on its side with tasty food at one end and see if he walks in then lift him out in the mug (you'll need to put your hand over the end before picking it up or he might leap out).
Then let him out in a playpen area for taming. I used the skyline ranch pen thing that I have. I thought it might be a bit big but it was fine. He enjoyed running around and exploring and ran over my legs (so familiarising) and actually ran up my trouser leg! Lol.
Before that I had tried a taming box - a not too large, rub bin, but that didn't help as it was a bit like a cage with a hand coming from the top, so the playpen was better.
But Nugget was so scared he would literally run behind his wheel and wedge himself between the wheel and cage side, flat, so you couldn't pick him up and was too savvy to be tricked by food! I had a hectic time when I got him and never did get him tamed.
So I think if you can get to a stage where you can get him out of the cage without stressing him for playpen taming, then you will have a good chance of taming him so he trusts you. There is a very good piece on taming robos below and it reckons they can be more tame than syrians once tamed.
What I did find was once Nugget was in the playpen I could actually pick him up - I would just sort of scoop him and turn him onto his back and hold him gently but securely. He would not move once picked up, and I could then have him sitting on my hand and stroke him. But do it with your hand very low down and over a cushion because they can suddenly leap off and might hurt themselves if they fell too far.
That to me was the turning point with taming - but unfortunately it didn't progress as he got cancer. It was actually more about me having the confidence to try and pick him up - once picked up he was more relaxed.
Have a few toys in the playpen as they seem interested in checking things out.
Re your tank - assume the wheel is on a platform or something?
The Roborovski's Dwarf Hamster