Hand baggage clears customs at the first entry point into the EU, even if there is no visible customs presence. If they are looking for someone they'll put a customs officer at the end of the airbridge (I see this at AMS occasionally). If they're not looking for anyone they'll just let everybody walk through.

So - whether you see a customs officer or not, your carry-on is deemed to have cleared customs at your transit point, and if you are arriving at your final destination without checked baggage you can go through the blue channel (if there is one).

Can't comment on the specifics of T1 as I've only ever arrived there from outside the CTA, but if Irish and Channel Islands flights arrive in the same place as international ones then I can't imagine there not being, at the very least, an invisible Customs presence - especially for Channel Islands flight, seeing the Channel Islands are outside the EU. The airports I've flown into from Ireland or the Channel Islands (LCY/STN/SOU) all have a common baggage hall that all passengers get funnelled into after they have cleared or bypassed Immigration.