The practical answer is, island hopping does not get you any credit towards the experience requirements for oil & gas.
If I were to put my aviation advisor hat on, when making hiring approval decisions, if you have <500 hours operational flying experience in oil & gas = co-pilot only. If >500 hours = Offshore Captain qualified, assuming ticks in all the other required boxes.
Island hopping experience might get you the nod over another co-pilot applicant who doesn't have any over-water flying experience, all other things considered.