A cat walk should be an acceptable work surface provided it meets a few requirements. I’d say it needs to be strong enough to support worker plus weight of tools/equipment and supplies, needs to have acceptable railing (otherwise they’ll need fall protection), and needs to have adequate access path for getting medical responders up there if needed (or escape if there is a fire for example).

Working from a ladder is never great if force, lifting, motion is involved. Scaffold or a lift is preferred. Securing the ladder helps, however it’s still a poor work surface. Need to make sure the tie-off points are properly located. This is dependent on whether you use retractable lanyards or not.

Could the crane touch the workers on the catwalk? If yes then need to LOTO the crane.