The only concerns I have ever heard raised about pools and pregnant women don't apply until after your water has broken. As long as your amniotic sac is intact, your baby is comfortably protected from all of the nasties in the water. I LOVE swimming while pregnant because it takes ALL the weight off of my back. We stayed in a hotel a couple of weeks ago and just standing in the water felt so good because it gave me a break from lugging around the baby weight I would start slow if you plan on swimming laps or something but your body will let you know if you are working too hard
As for the whirlpool- sitting up on the edge and just letting your feet soak feels great You are right though, getting in all the way is a no-no.