You can use an ETZ250 rim with a TS250 rear hub but better to use a the wider rim from a rear ETZ wheel as the front rim is really only wide enough for a 3.00″ tyre.
You will probably find that surgery is needed on the centre stand cross piece depending on size of tyre fitted. You will also probably find it overgeared with the standard 20t sprocket and need to drop to an 18t.
Another option is to find a complete ETZ250 rear wheel and sprocket carrier. This will fit staright in and can make use of your existing chain and chain rubbers. Saves having to build a special hibrid wheel.
Did you use the ETZ chain cover as well? The TS cover is not compatible with the ETZ sprocket carrier assembly. My ES250 trophy is running with an ETZ back wheel assembly and I don’t recall any problems fitting it, certainly did not need to change the stub axle.
For some time I had a supa5 rear wheel and sprocket carrier in my ETZ250, when the original wheel was damaged. It fitted straight in, although I believe the assembly is displaced by a millimeter or two.
Vee Rubber and Mitas make 16″ road tyres which are very cheap and quite well regarded by many people.