I can't answer the question about scallops directly, but I can address the diving in general.
San Jose is inland a little ways, but as stated before, it is just over an hour away from some of the finest cold water diving anywhere. Definitely world class.
In Monterey Bay the vis is not great. Often you can only see 15 or 20 feet, but you will see a TON of stuff in that 15 feet! The vis is usually a little better in winter than in the summer. It can get to 50 feet or more on occasion, but plan on about 20 feet.
The water temps range from 40's to 50's typically. Temps are a little lower closer to Carmel and Pt Lobos, and a little warmer in Monterey. Also the water temps tend to be a little warmer in winter than in summer. November is a great time to dive Monterey Bay area.
The best diving areas are within the wildlife refuge, so many of the animals are protected. Howver it is a great place for taking photos.
Santa Cruz is a little up the coast from Monterey, and a little closer to San Jose, but there is very little diving done there. It is less protected from the currents and weather and swells, and for some reason no one seems to dive there. I hear that there just isn't much of anything to see underwater near Santa Cruz.
In addition, there are a lot of cool things to see and do and eat in the Monterey Bay area above water.
Adding my bubbles, but only because you asked.
Wristshot