Technically, you can put them in the R slots, but they won't function. The only supports that can go into R slots and work are engies and reps. Besides, seamen are a waste of space. You don't need them on a CV.

Yes seaman will work on the gunner slots. Reps also work. Engies do not work.

The seaman ability adds X amount to all other sailors' abilities on the ship.

- It doesn't matter where the seaman is sitting, and seamen DO stack, but more like engineers, so there is a diminishing return.
- Seamen also add their own repair and restore to a ship, and that value is hidden, much like a Bridge Officer. Presumably, the seaman boosts his own repair and restore skills.
- Seaman ability is not capped, but they do not allow other sailors to exceed their skill caps. So while a lvl 120 boosted Seaman with 300 vets can make your level 80 fighters behave like level 110 fighters, it won't help your level 120 fighters much if at all.

Seamen are therefore most useful to fighters in the 60 to 100 level range, allowing them to suck less. I've also noticed that 5 identical engineers plus a seaman results in more overheat time than 6 identical engineers, because of the limitation on how engineers stack. (And that 4 engineers plus seaman is about the same as 5 engineers, but it's still better because that seaman is boosting everyone's repair skill too.)

A short while back, there was quite a bit of testing and discussion of what seaman do.

If you put a seaman on a CV, ideally you want that seaman to have higher F, B, & aircraft stats.

The seaman boost is a percentage boost, not an ability add.   The seaman numbers are not a straight percentage but a function.  i.e.  a fighter ability of 15 is not 15% but a boost of perhaps 1.5%.

Testing showed that seaman tend to be specalists, boosting abilities more in one area then another.

In testing, it was impossible to tell how much seaman helped pilots as there were too many variables.   However, testing found that seaman helped performance in other areas so there is reason to believe they help pilot performance.

The statement that they don't seem to help much at higher levels rings true.