You always must use wired-on (versus folding) tires with hookless rims. There is usually no reduction of the tire's rated pressure when using such "straight-walled" rims, though some vintage rims (from Weinmann in particular) were known to have slightly too-small of a bead-seating diameter for the tire to be safely inflated to rated pressure. It was more of a quality-control thing in my opinion, since some pairs of rims had one that could take pressures and the other that could not.
Quality control problems more often arise with OEM rims, since QC corners are cut when the buyer negotiates for lowest prices.

Some rims are stamped "W/O" next to the manufacturer's markings, usually near the valve stem (it stands for "wired on").