Oscar, that's a good question. The difference between male and female flowers on rambutan is very plain to me. However the hermaphrodite flowers I am not too sure about. Also, can't there be male/female trees that have both kinds of flowers individually? I've never actually noticed this either.
My comments have to do with my experience of simply running into lots of male rambutans and very few male pulusans. Maybe that's how it is generally, or perhaps it has to do with the introduction material. Even though there are a lot of rambutans in CR it could be that the original rambutan seedling material introduced into Golfito by Chiquita has been the source of almost all the seedling material.
More recently a lot of select rambutan material has been propagated and the older, sometimes called 'criollo" stuff is being forced out of the market.
Pulusan is still a minor fruit although rambutan is huge.