I guess that if it was a charter, it had to be VFR all the way anyway (Single engine commercial with pax according EU OPS).
EU OPS only stipulates no single-engine IMC or night. There is nothing to stop operators flyiing single engine day IFR in VMC.
However, remember also EU OPS regulations are only a recommendation to member states. Member states are free to opt out of some of the regulations and several have in order to allow specifically PC12 operations. Given that PC12 is manufactured in Switzerland, I suspect that Switzerland is one of the countries that allows PC12 operations.