Thanks for already saying you’ve gone through the previous posts, saves me saying to do it 🙂
You are more than suitably qualified to get started with ROVs. Yes,having a bit of hydraulics experience/qualifications would certainly help. Although when you start in ROVs you are broadly classed as either being Electrical, Mechanical or Hydraulic.
Most of the larger Workclass vehicles have high voltage/heavy power requirements meaning a lot of work required on the electrical side, dont think that ROVs are all about the mechanics and hydraulics. In fact if anything they are going more towards electrics all round these days.
Have a look through the section in the FAQs on "How To Lay Out Your CV" and use it to tailor your own CV and experience and start getting it out there to the companies. Most of the Major companies take people on and then put then through an ROV training course so I really would just try applying direct rather than possibly spend thousamds of pounds of your own money on a training school course.