Granted, I have not been to Raja/Triton Bay, but been to plenty of other places in Indonesia and this is first time I hear about service charge being mandatory, at least I certainly did not notice. But perhaps I hang out around more peasant places. Or maybe its also a regional/regency thing.French journalist/diver article on Triton Bay Divers if you can read french or accept autotranslation in english (click english button in the menu).
You can also browse her other divetrips once you're there, it's quite complete on Indonesia.
Triton Bay : fabuleuses plongées sous les cocotiers (Kaimana, Indonésie)
Le plus gros danger sur cette île de Papouasie, c'est de se prendre une noix de coco sur la tête ! Et d'en prendre plein les yeux sous l'eau...petitesbullesdailleurs.fr
As for someone living in the EU asking, service charge is mandatory for hospitality businesses in Indo, 21% is often charged in Indonesia for hotels : (11% kabupaten hotel tax + 10% service charge ) service may vary from 5% to 10% (likewise in many countries of the EU charging service in their bills, Belgium for instance).
Therefore you'd normally needn't tip, but then it's up to you.
Interestingly Trip Advisor calls it "the other 11% is a legally unenforceable service charge". And 10% is the "Hotel and Restaurant", which is actually mandatory, but in turn VAT does not apply at all.
Indonesia: Tipping & Etiquette - Tripadvisor
Inside Indonesia: Tipping & Etiquette - Before you visit Indonesia, visit Tripadvisor for the latest info and advice, written for travelers by travelers.
www.tripadvisor.com
But in this case this answers my question, hidden service charge really. And this is curious, since Indonesia regulations on service charge stipulate that 95% of it needs to be distributed to the employees...so yeah, cynical me want to see that one happening.
As for service charge in Belgium I have no clue (don't speak a word of the lingo) but my impression was always that it is up to the establishment to decide whether to charge such or not. Certainly this used to be a case in UK. And such charge was always optional (as in could have been refused by the customer if you want to make a lovely scene )
Anyways, all I wanted to have is some clarity. If there is a service charge, fine, but make it clear, don't hide it under taxes and then list gratuity under "not included".