I have two little Roborovskis, of course they are the smallest of the hamsters and I find they have trouble just climbing into their ceramic food bowl and that Syrian could easy walk into
Unless they have something the climb up to the top of the tank I dont think they are going anywhere. My Roborovskis are about an inch maybe an inch and a half tall when they stand on their hind legs. I havent seen them jump yet so Im unsure about that.
I guess just to be safe, make sure that any tall objects in the cage have about a 5 inch space from the top of the tank.
If you still worried you can buy a mesh tank topper that you often see used for reptile terrariums. Also keep in mind that they could climb up hanging watlle bottles. So maybe you should just get a tank topper?