Disclaimer: I have never flown Ryanair.
As far as I can tell, there is no security check for these items. They are put in a compartment right at from the gate and are usually taken out and placed on the jetbridge or around. The assumption seems to be that it has passed security, so it should be good. If an item poses a risk to be stored, you really should tell them.
This is something I have seen with other airlines many times though. They usually go around and ask everyone with the largest carry-on to check first. In most cases, after they collected enough of these, they stop. Having a smaller carry-on greatly helps and they almost never ask for mine. Less than 5% of the time, I do get asked which brings me to my second point:
Make you carry-on ineligible for hold storage. They are many rules (some by the airline, some by the authorities/security) limiting what is allowed in checked luggage. For example, nearly all flights within South America do not allow electronics in checked luggage. In this case I tell them or show them what it is and they let me with the bag. Another thing is that you may need essential medicines or medical devices and that has priority.
This does not guarantee you will never had to gate-check your carry-on but it has served me to follow these rules:
- Smaller carry-on than others.
- Carry expensive electronics.
- Have life-saving medicines.
- Be polite and apologetic if you feel that complying would be risky.