It is difficult to make an assessment of a situation like this with a few photos and the description given. Based on your statement that the contractor has an excellent 30-year reputation, we’d suggest you discuss these concerns with the contractor. If his response does not give you a full explanation, we suggest you engage an independent professional familiar with shotcrete installations and swimming pools to give you an opinion. You can use ASA’s Buyers Guide at www.shotcrete.org to find a consultant.
There certainly is reason to question the quality of the installation based on the description. However, it is not unusual for the pool shell contractor to leave a temporary opening in the shell to relive potential groundwater pressure and prevent floating of the empty pool shell. These holes are, or should be done, in a professional manner to allow complete watertight sealing when filled. In some cases, the openings may include a pressure relief valve.