My understanding is that it is the kernel that evolved into the current kernel. IBM likely modified it quite a bit and MS may have had functions in it that were removed. Trapping int0x21 calls is one possibility as MS was planning on supporting Win16 apps similar to NT's WOW, with WLO so they would have run more native then IBM's solution.
The compiler etc probably aren't very useful, LX binaries weren't even supported, and they were beta quality. Though IBM may have used the cl386 compiler for the kernel.
You could always ask on
http://www.os2museum.com/wp/the-future-that-never-was/, Michal is pretty knowledgeable and usually answers comments. It is where much of my incomplete knowledge comes from.