Vita) offer just as much input dexterity as their shelf-based counterparts, if not more so, to the point where developers are able to expand and experiment with their control paradigms.
The Vita port of Marvel vs. Capcom 3, for example, makes use of both the device's touch screen and its rear capacitive touch panel for movement and attacks. Moving your finger horizontally along the back panel moves your character left or right, moving it down makes them duck and moving it up makes them jump. Attacks are initiated by tapping the screen, and hyper-combos are triggered by tapping the hyper meter; assists are called in by tapping the respective character's icon.
It sounds like an awful lot of furious tapping and awkwardly loving strokes along the back of the device, and considering that all of your characters' meters could be on the left or right side of the screen, a bit of ambidextrousness may be required as well. Fear not, however: Conventional control methods will be included at no extra charge.