My guess is that they have taken marine-trained people and made them enviromental officers because it is a newish position, but that as time goes on there will be more people who specialize in this kind of stuff.
I also suspect they go through far more IT people than environmental officers, therefore your chances of getting hired for a first-time jobas an IT person are greater than as an EO.
I also think that the EO job would get rather dull (personally) since every day would be monitoring bacteria levels and making sure the incinerator os working correctly - and lots of writing reports. Might be very easy, however.
I don't know any EOs. but I have interviewed a few. They seemed pretty easy-going, like their job was not much of a challenge - uhnless things screwed up, of course.