Although at first Dead Aim seems like its own sidestory, post-Code Veronica games make it retroactively important to the series. To quote Thomas Wilde's plot analysis:
"Looking at RE:DA in light of the post-Raccoon timeline established by RE4, RE5, and RE:UC, it makes a weird sort of retroactive sense. In 2002, as per RE:UC, Umbrella is fading fast and spending most of its remaining money on attempts to keep the various legal actions against it tied up in court. The Spencer Rain, as a mobile auction block for Umbrella, could be seen as an attempt by the surviving executives to generate some quick capital towards their legal defense, since it's the first time in the series's chronology that Umbrella's ever been seen selling its bioweapons.
It also means that in a weird way, Duvall is partially responsible for the fall of Umbrella. An early file on the Spencer Rain indicates that the ship was full of high rollers, there to bid on Umbrella-brand bioweaponry, and Duvall killed them all. If he hadn't, Umbrella might have actually made enough money to defend itself in court."
