Absolutely. They also have a limited variety of Mountain House FD items.
Caveat: Inventory levels can fluctuate widely. There are a lot of campgrounds there and an overabundance of hikers. The place could get cleaned out an hour before you get there.
Fortunately, its not difficult to get into Mammoth Lakes and back. Don't pass up the awesome café next door (reservations required for dinner) or the laundry behind the bathrooms. Cabins, if available, are worth the expense if you have a small group.
If it really worries you, send yourself a resupply box there. The store will hold it for you.