I can see there being a big difference in death rates between, say, an Alaskan crab fishing operation and a suburban CPA firm, but 'job' is one of the questions that's asked by life insurers so that's already accounted for.

How would a white collar office employer legally engineer a higher death rate for their people than an equivalent company down the street? Providing only fries and burgers in the canteen? Relocating to an office block near a chemical waste plant? Nothing really seems feasible or effective enough to make a measurable difference to the performance of the investment scheme. The added investment return bought by shortening the lives of some percentage of staff by a few years would be just noise compared to the tax savings this vehicle provides.