ALIP provides the needed files for booting up the Beagle board and OMAP 3 EVM. Do not expect product quality from these.
The OMAP based platforms contains two repositories, one for platform specific components and one (called "omap") for OMAP 1/2/3/4 specific components. The binaries needed for booting an OMAP3 based board (x-loader, u-boot and the kernel) are built and installed to /boot inside Scratchbox. Kernel headers for user space applications comes in a component called "kernel-headers" and that is provided by generic platform (it can be overwritten by the platform, when needed).
Note that all the components in the omap repository uses the same branch as the platform specific repository. The branches may or may not be identical to other platform specific branches. The branches are versioned in the same manner as other repositories (beagleboard-1, etc).
And the same in a list:
Although the above description talks about OMAP3 based boards, the same logic should be applied to other BSPs for ALIP as well (the components in omap repository might be merged into platform specific repository).