No one else seems to have taken a stab at this, so I'll give it a go. Maybe it'll encourage someone who has the difinitive answer to post.
A hooter is carried on a spinnaker pole, while a Genoa is attached to the forestay, like a working jib, only that the clew comes further aft. Relative to the working jib, I believe a hooter is larger than a genoa. They are also lighter than Genoas.
Hooters seem to be more like spinnakers in construction than jibs. They also are primarily designed for off-wind performance. Not knowing much about sail design, that would lead me to believe that they are cut fuller than Genoas.
For more info on hooters, see catsailor.com/update_hooter.html