Yes, provided that you’re flying with American Airlines that day. You also get your two free guests when using your Citi Prestige card.
The Airspace Lounge at San Diego Airport (SAN) is functionally an Admirals Club in terms of access rules, with the addition that you can get free access (plus a credit!) if you use an Amex Platinum card. This means that you can still use your Citi Prestige card to get access when you’re flying with AA, even though it’s not named an Admirals Club. If you’re otherwise eligible to get access via multiple ways, you should choose to use your Amex Platinum card because you get a food and beverage credit.
While the lounge functionally has the same access rules as a normal Admirals Club, the free food options are much sparser. I’ve been enjoying the steel cut oatmeal available at Admirals Clubs in the mornings, and that’s nowhere to be seen. Instead, they have two snack towers, some oranges and apples, and some mini muffins for breakfast.