Definitely been covered a lot of times.
No, they don't behave in the same way. Irish moss coagulates proteins (i think?) during the boil. Gelatine helps pull the yeast out of suspension after fermentation. So no, irish moss wont flocculate yeast, because there wont be any yeast in your boil.
Gelatine will help some of your yeast fall out of suspension. There will still be plenty left to carbonate, as you said, so not sure why you asked again.
I use Brewbrite in the kettle and thats it. Cos it works well and is easy to use.