ViviTouch technology doesn't require developers to use an API to generate vibrations. Instead, it converts game audio into a variety of different effects. For example, clicks or the sound of a pinball bouncing off a wall, will make one "feeling effect", while shooting a gun might make a different one. There is also a subwoofer mode that creates a vibration when low-frequency rumbles are heard. There IS an API that developers can use to optimize their games for ViviTouch.
Mophie, the company actually putting the technology into production, is the same outfit behind the excellent Juice Pack extended battery cases. The company has a sign-up page to get notified when the Pulse launches. Mophie promises the Pulse is "coming soon."
Hat tip to Kotaku.