I think to have a pet in the passenger area, the pet would have to have seeing eye dog, or other people safety assistance registration.
& I would expect the ferries to explain it all in terms of boating safety procedures.
The older ferries had a kennel option, one which I tried once and found my dogs didn't like at all in comparison to remaining in their usual travel options. They much preferred to stay in a place they knew well.
I also found that crew paid attention to pets, whether you told them about your pets or not. I got quite used to coming down to my rig at the end of the trio and being told what great dogs I have.
:)