If it's of help, I've submitted some pull requests upstream to improve
their debian folder:
https://github.com/FreeRADIUS/freeradius-server/pulls?q=is%3Apr+author%3Amans0954
#1256 is probably the most critical, although that only affects a couple
of the optional packages. The rest are mostly about reducing the number
of lintian warnings.
The HEAD of the v3.1.x branch now builds and installs on Jessie. I
didn't see any systemd warnings, and the daemon runs for me. I haven't
tried any testing beyond that yet though.
I'm assuming that one of the existing maintainers/uploaders will be
packaging v3 in due course?
Christopher