From the S-1: "We use DRAM ICs produced by Samsung, Micron and Hynix in our DRAM modules. We purchase those DRAM ICs, pursuant to purchase orders and not long-term supply contracts, largely from third-party distributors and, to a lesser extent, directly from those manufacturers."

Edit: And "We maintain limited manufacturing facilities that only produce DRAM modules, custom built PCs, custom cooling and performance controllers, and as a result, we depend entirely upon third parties to manufacture and supply the gear we sell and the components used in our gear such as gaming peripherals and gaming components." So they do actually manufacture the modules in-house.