Yes, ubiboot is a loader kernel. It is not a "user-kernel", in a way that it is meant to be a boot loader 1st stage, which then launches your "real" kernels which run your OS. Think of it like Grub or LiLo, or Uboot. Under ubiboot, you then select/load the 2nd stage kernel, this can be plain open mode kernel, old-style nitdroid kernel, enhanced kernel+NAT, enhanced Nitdroid kernel, whatever. Ubiboot is just the method to select between all these kernels (and of course the OS that the kernel runs, as default it can be Harmattan, Nitdroid or Nemo. Later maybe something else too... FFOS, SailfisOS, Tizen,...)