You only need libxml2-devel to (for example) recompile libxslt.
All you need for nsxml.so and OpenACS 4.x is libxml2; however, when I asked about the need for libxslt support, I was advised by folks here to put libxslt support into my RPMs -- some folks think OpenACS 4 may eventually use some of the XSLT stuff, either by default or when some OpenACS 4.x users want to customize it to do so.
Grabbing the libxslt-1.0.3 SRPM and recompiling it doesn't take all that long.