"Yes, there is DRM," the admin confirmed. "This was employed to combat the rampant 'PSN Sharing' that has been going on over the last year. We're sorry that your family cannot play the game on their individual accounts (same console). This is a limitation of the Sony network." The message goes on to say that Double Impact's DRM is a trial to "evaluate impact" of the PSN sign-in requirement, which seeks to limit access to the game to the PSN account that purchased the title.
Since the statement was posted, Nacthenud and others have discovered an apparent workaround. They suggest it's possible to play the game using secondary accounts on a PS3, provided the account used to purchase Double Impact is set to automatically sign into PSN when the console turns on. But that's ancillary to the intended purpose of the DRM: to prevent users on other PS3s from playing the game (and thereby rendering the game unplayable offline).
We've asked Capcom for verification, but have yet to hear back.