I wouldn't want to pee on a fish directly but if the tank was like under the urinal water and "looked" like you could pee on the fish thats a little different. If this urinal has a constant flow of water the fish should in theory be fine there shouldn't be a ammonia build up to toxic levels. but still very stupid.
On a side note about urine's sterility I heard that if lost in the desert you can drink your urine 3 times before it gets to toxic and has adverse affect on you.