Whispers and hints from the developers allow us to assume there'll be some kind of multiplayer in the Vita-sized versions of the PS3 titles.
[Update 1/25: In the original version of this post, I erroneously described Naughty Dog as the devs of Golden Abyss. This has been corrected to reflect that Sony Bend is responsible for this title and that it is launching on February 22nd.]
Over at Destructoid, while talking about his hands-on time with both Uncharted: Golden Abyss and Resistance: Burning Skies, contributor Maxwell Roahrig says that while getting in few words with developers Sony Bend and Nihilistic Software, he was able to glean some additional details about each games' respective multiplayer.
He was was able to confirm that both titles would have it, although it's unclear what shape it would take for either game. Speaking with the Sony Bend rep, Roahrig was able to extract only that whatever was planned for Uncharted, it would be "something different." Meanwhile, Roahrig reports that the Resistance team at Nihilistic were looking to replicate the console multiplayer experience, meaning many of the modes in the PS3 version are likely to make an appearance on the handheld.
Uncharted: Golden Abyss will be hitting during the Playstation Vita launch window, February 22nd, while Resistance: Burning Skies is due sometime later this year.