I finally got pd to connect to jackd when both are started as user, and in conjunction with the realtime-lsm module running as modprobe realtime gid=xxx. All I did was compile pd-0.38-0 without the --enable-setuid flag!
would it be possible that you test devel_0_38? it's possible that it's a problem with the memory locking... hard memory locking only works correctly as root ... i implemented a workaround to devel, solving another problem, but it might be related to that ... the stable branch isn't using the memory locking correctly, which may result in a segfault ... this is a bad bug, which is easy to solve ...
cheers ... tim