Offshore is exactly that, and if you are island hopping then that is offshore.
It is up the company hiring to differentiate between the various offshore flying that could take place.
Some might want a certain amount of platform landings, others might want ship landings the list goes on.
I would be putting in your island time, at the end of the day you have done it and unless they have specifically asked for OGP type offshore you haven't mislead them in any way.
There will be a lot of people ready to tell you it doesn't count unless it's OGP type flying because that is what they have