Can optometrist be relied on to diagnose glaucoma? Said I didn't have it yet but would watch it. Glaucoma specialist said I have it at moderate stage

No! Only an ophthalmologist has the training and experience to diagnose, monitor and treat glaucoma. Early glaucoma can be very subtle, and optometrists do not have the medical background or level of experience to distinguish early signs as glaucoma usually presents with no symptoms.
It depends. For all professions there are different levels of training. In some states, optometrists may receive additional training for glaucoma evaluation and initial treatment. All ophthalmologists will receive glaucoma training through their residency through both clinical experience and lecture/books. Optometrists usually refer more advanced glaucoma patients to ophthalmologists. A 2nd opinion helps.
Good question. Optometerists don't have the level of medical training a physician has. Obviously I am biased. I think a third ophthalmologist opinion is needed.