Can I build a concrete block wall over floor tile?
The tile floor shouldn't be a structural weakness, but if it's glazed you won't get a good mortar bond. I'd install anchor bolts every 32" or so, aligned with block cores, and fill those cores with mortar. 

It might be easier to simply cut the tile inside the wall line and remove it, though. 

Also be aware that your slab may not be designed to carry a heavy wall. If it doesn't have proper footings underneath it may crack and settle.