Yes, they are visible to the enemy. It's part of his counter-play. Does hurt his gank potential, but really he has terrible clearing so he probably shouldn't jungle. I had issues just clearing a lane when I dropped him in a custom game to check his soul gains. Clearing the jungle is even worse. He is a fantastic support and could work as an AD bruiser top lane (yes AD). His AP ratios are absolutely terrible (minus ult) and when you build him AD the Q passive hits like a truck.