It depends on the company. I know that one of the big ones pays all its staff via the UK, while I believe another of the large companies can pay locally and with IKA for some office staff. Some may offer a choice and others not. I know a number of people who work for small tour operators and have IKA paid, it all depends what they - and you - are willing to negotiate. Some people pay the IKA for themselves through the tour ops agents if the tour operator themselves won't do it.
Officially if they are a UK based company and you are hired as seasonal staff they can pay you via the UK payroll and do not have to pay IKA here.