Growing up I had a family friend who was a park ranger in a popular hunting area (not California fwiw). The laws protecting wildlife from poachers are really strong and rangers take them very seriously. As a result, catching a poacher can often be a messy scenario. If it doesn't turn violent, you can bet the poachers will try everything to get out of catching the case. I don't think it's unreasonable that poachers would try to protect themselves with this defense.

That said, I don't think that potential wiggle room poachers may try to exploit should be reason to keep salvaging illegal. The only time I have ever heard of a poacher making that excuse was in an askreddit thread (yeah I know take it with a grain of salt) about LEOs getting guns pulled on them. In that story the ranger could clearly tell the animal had been shot, not hit with a vehicle, and I would imagine in many other cases a ranger would be able to tell the difference too.