Hey Warge,
I can assure you that swimming with an ostomy is not a problem at all. The appliance are designed in ways that allow you to stay in water for a long time. Preferably you need to empty your bag before you go swim (for aesthetical and comfort concerns), but you can swim as much as you want.
The hardest is to find a swimsuit that satisfy you. I have "hard" time because I'm a woman and it would already be hard without a bag. I don't consider it to be a terrible chore even dealing with it and worst would come to worst, some people just deal well with wearing which ever swimsuit they like no matter if the bag shows or not.
The bag and the appliance don't break or what under the influence of water or long time water exposure. So spa, bath, swiming, etc are still totally possible =)