Hi mylucky666, welcome to Cruise-Chat. I've not had the pleasure of doing a river cruise, so can't answer your question, but did want to welcome you aboard. Cruise Fanatic did a river cruise recently, so hopefully she'll see your post and can answer your question. Hope you have a marvelous adventure, and once again, welcome aboard!
Scylla is a Swiss owned company. I am not sure how their tipping policy would be. I recently did a Danube River cruise on an American owned ship. The crew all were European. The recommended tips for them was about 10 Euro per person a day. The tips were pooled and divided among all the crew.