If I ask Jenkins (or lsstsw) to build skymap the optional dependency of healpy is not included in the build. If I try to build afw it does include the optional dependencies of pyfits, matplotlib and afwdata. pipe_base does bring in its optional dependencies as well.
I haven't worked out what is "special" about skymap.
For an example Jenkins build: https://ci.lsst.codes/job/stack-os-matrix/label=centos-7,python=py3/14837//console