Just lost an Excise Vault because two snipers were spawned on the upper catwalks. As a Veteran I used my special ability to highlight them and counter-snipe them, but it is ineffective. Scab Snipers are allowed to fire through the catwalk grating, but my Mk12 Lasgun could not hit them despite over a dozen well-aimed shots at both.
Theoretically plasma guns or bolters might be able to go through the geometry to hit them, but at the extreme ranges involved on that map, it’s unlikely that is the intended counter method or indeed, even possible at all.
TLDR: Scab snipers can fire through geometry like catwalks that players cannot. This makes an already serious threat almost insurmountable because if you try to climb a ladder etc. you will be sniped before having direct LOS.