*FACEPALM*
What JdGordon likely means is that OpenOffice is written in a weird mix of C++, java, javascript, and other languages, for an environment where using another ten megabytes for something is not a problem, and that as such trying to re-use parts of the OpenOffice code in rockbox is likely to only result in lost time and frustration.
As such, the fact that OpenOffice is open source is totally uninteresting.
You could of course find other ODF implementations that are slightly smaller. Keep in mind though that rockbox is GPLv2 or later, and that such implementations should therefore also be under a GPL-compatible license (not just any open source license). Also, rockbox is written in C, and although it may be theoretically possible to get C++ code to work, the general consensus is that this also isn't worth spending too much time on, so such an ODF implementation should ideally also use C.