Not only do the kernel patches for using freeswan doesn't work on sparc (AFAIK, sparc32 and sparc64) but the package sys-kernel/crypto-sources on witch freeswan depends, has a -sparc mask. (this only applies to versions 1.98b and 1.97)
Marking this as resolve:later as we currently don't have any kernels with the appropriate patches to handle this. Hopefully this will change in the future when the appropriate patches play nice with sparc.