Great, but I won't use, because I don't need it, as least not now!
uma0 is where the usb stick is registered at after you run vitashell to mount the usb stick, before you can mount it to "ux0".................Good if you have vita memory card and usb stick, "henkaku enso and "usbmc (to automount usb stick at startup)"....................you won't have to mount the usb stick to ux0 to play the pspemulator just mount it to uma0 with the psp memory card still mounted to ux0...............I think thats right?
(just like many people, i've been using the psp memory card for psp/ps1 only and usb stick for vita games, just been the most convenient option) (do you need to change anything in the henkaku boot file for this change when playing from uma0, never gave it a second thought until now)
EDIT
Just created a iso folder and added a game in the usbstick when it was mounted at uma0, adrenaline does not pick it up, guess since its currently installed in the memory card from the traditional installation of adrenaline..................needs another installation method to work for uma0 (henkaku enso with usbmc will can bumb the usb stick to ux0 at book, and then the traditional install methods for adrenaline will work and you won't need uma0, so you see, this method is somewhat troublesome of using "uma0" partition)