If they are just spraying gunite though the cage to coat the dirt, only a light coating is getting on the rebar. Which will then be totally encased when the pool is gunited.

I doubt this would be in anyway negative to the completed pool.

Sounds like an ounce of prevention on the builders part to me.

I hate to imagine the hassle of clearing a collapsed dirt wall out of a pool with the rebar already positioned and wired.