Actually kernel does not need uClibc.
But the user apps do.
The nios2-linux-uclibc-gcc is the same compiler as nios2-elf-gcc. But we build it (using buildroot) again uClibc for uClinux instead of the newlib. The nios2gcc.tar.bz2 has uClibc already. So we don't use the uClibc build in the uClinux-dist.
But you can still use the uClibc of uClinux-dist. You can use nios2-elf-gcc and need to add nostdinc, nostdlib and crt0.... flags to arch.config . You can find these flags in the make rule of Microtronix's 1.4 release or the other arch in uClinux-dist. That's what we did without buidlroot.
There is a "debug" apps in Microtronix's 1.4 release.