Yes they can get "cage rage" in those little plastic cages. But he is doing really well if you've only had him two weeks. It's time and patience, especially if he's had some rough handling previously.
Hamsters only bite it they are scared or if you are hurting them. They learn to trust when you are gentle and respectful of them and they will get to know your scent and can also bond with you. Taming can be a bit slow or it may happen quickly and they are the easiest to handle when they have bonded with you, know you and trust you.
So keep going with offering him treats etc and keep talking to him gently so he gets to know your voice.
On top of all that they are naturally territorial in their cage and often don't like a hand in their cage - they see you as a possible predator in their territory or just an invader who might be there to steal something! Food or their carefully hoarded little pile of hidden poops for example (they actually eat their poops sometimes, which is normal - they have two stomachs and can redigest nutrients, and some hamsters will have a secret pile of poops as emergency food supplies). So don't worry about cleaning those out much for a while - they're not dirty or smelly - more like little hard seeds.
Another thing that can set taming and trust back is too much cleaning out. Pet shops often say weekly but it really isn't necessary in a good sized cage. And that is another problem with the current one - there won't be much room for deeper substrate and the cage will get messed up and need cleaning. So it can be a bit of a viscious circle as cage cleans really stress them - especially in the early weeks and if everything is cleaned at the same time.
So for now maybe try and do the bare minimum - just "spot clean" the pee area - take a handful of substrate out and add a new handful and mix it in and try and leave his nest alone/in tact. They get upset if their nest or hoard is removed - if you do have to remove it if it's pee;d on then always put some new food back in the same place (ie replace the hoard).
And I'm not sure how the habitrail is set up but try and have as much substrate in as you can.
So basically they are easier to hand tame out of the cage than in it. A good way of getting them out if they hiss at your hand is lower a tube (eg toilet roll inner tube) in and let them walk into the tube, then lift the tube out with your hands over each end - but you need something very closeby/next to you, to put the tube down in again - eg a large cardboard box or plastic storage bin so he isn't trapped in the tube for more than a few seconds. Some hamsters will be ok with a taming bin like that - others hate being in a box and are better in a larger area like the dry bath tub or a safe playpen area, for taming. But you can carry them in the large box to somewhere else where you can let them out for taming.
If you have a bathtub it can be a good safe area - with the plug in and dry and a few tunnels or toys and hidey places (cardboard is fine - tubes and tissue boxes eg). And he can run around in there and gradually get used to being fed from the palm of your hand, walk on your hand, be stroked etc, with the stages Souffle mentions above.
Cagewise - you would be much better just making a good sized bin cage than adding one onto to the Ovo. One larger cage works way better and allows them to have normal behaviours. The Ovo really isn't suitable for any hamster to live in. It can also be quite difficult to attach it with tubes without it being an escape route. But not impossible. If you have an Ikea nearby, the 78cm Samla bin is a good size for a dwarf hamster and it's cheap.
You need at least 4" depth of bedding in a cage as well - more if you can, so they can have normal behaviours like digging and burrowing and pushing the substrate around (they like to busy themselves doing that and making little mountains out of it and hiding things under the mountains
And a house in that is dark inside as they need somewhere dark to retreat to that's big enough to build a nice big cosy nest. They also need a sand bath. A dish with Chinchilla bathing sand in - and will often use that as a toilet as well. Plus a suitable sized wheel - minimum 6.5" diameter and 8" diameter is good as well. Toys like cardboard tunnels and hidey places and ideally a shelf or platform as well (which is a good place to put heavier items like food bowls).
You will really notice the change in his behaviour when he has the space to have normal behaviours - and decide where to do things - they have favourite spots for sitting for a wash (often on a shelf) and have places to go and things to do with the variety
I made the same mistake with our first hamster - he was in a plastic rotostak thing and he not only had cage rage but was also lethargic and depressed. Although he was a bit shaky and nervy for a couple of weeks after moving to a bigger cage (the size of the Hamster Heaven that Cypher mentioned) that is quite normal with a cage change for the first two weeks. And after two weeks he was like a different hamster. You could tell he was happy and he almost looked to be smiling! Bright eyed and perky and just acting more confidently and very much busying himself in his cage.
I would say it is apriority to upgrade him to a larger cage or bin cage as soon as you can and not to expect taming to progress very well until he has that.