Yes, houses with septic tanks are bought and sold routinely in Ireland. Before purchase you should establish that the system is registered, that it has been maintained, and ideally that it functions properly, because remediating a failed system and percolation area can be a significant cost for the new owner.
Domestic wastewater treatment systems must be registered with the local authority, and registration details are usually raised in conveyancing enquiries. If the system has been inspected under the National Inspection Plan, any advisory notice issued and the works done in response should be disclosed.
A physical check is worth commissioning. Ponding or lush green growth over the percolation area, smells, gurgling drains or a tank that appears full to the inlet are all signs of a system that is not working as intended.