Zoanthids and Palythoa species (a zoa relative) can both carry a chemical called palytoxin to varying degrees, but they're not really poisonous to the touch. The toxin is an issue when:
1. They are cut, damaged, or really stressed to make them slime or squirt at you and...
2. You somehow get the toxin in your blood (like from a cut), ingest it, or get it on a mucous membrane (eye/nose/mouth)
Accidentally ingesting the coral's slime or secretions is the main way I've heard of people getting sick from palytoxin. So, don't sick your hands in the tank and then make a sandwich without a good wash with soap first. I've never heard of any instances of it being absorbed through the skin from simply picking up the coral. If you want to be 100% safe, use gloves. Never, EVER frag one of those without gloves and face protection - fragging requires a lot more caution than just poking around in your tank. It's a good idea to use that anyway on other corals that can also squirt you.
For my own tanks, the reality is that I am often sloppy with gloves for regular maintenance because I forget them and just dive a hand in. I have one of the more potent types of palys and have touched a lot with no ill effect - not because it's a good idea, but just because I'm thoughtless about it and go "oh darn shouldn't have done that" afterwards. However, I never put a hand with cuts into the tank and I ALWAYS wash my hands after they've been in contact with aquarium stuff. I also try to remember gloves, I just often forget - but I've never gotten sick from it with my marine tanks since I'm rigorous about washing up.
On a side note, there are plenty of other things that can make you sick from aquariums though, not just zoa/paly toxins. I learned that the hard way many years ago (long before I kept marine) from getting some water from a freshwater tank splashed in my eye and not flushing it out immediately. Had a horrible painful eye infection that took a couple weeks to go away and give me full sight back. Good hygiene and keeping anything tank related away from your face is very important with any aquarium and will keep you safe with regular maintenance with zoas/palys.