I wouldn't add the pineapple to the boil, I would do it all in secondary until the gravity stops changing. I think you'll get better flavor and aroma that way.
The main reason not to boil fruit is because it sets the pectin and gives you a permanent haze, but I seem to remember that pineapple has very little pectin. Plus I think it has an enzyme that breaks down gelatin, I'm pretty sure I read not to try to make jello with it.
Anyway, that's just me.