I do not think it really matters in pfSense builder case where you adopt git with FreeBSD or not.
Our patches apply to FreeBSD repo be it SVN/GIT/whatever.
Nowdays you can clone the freebsd git repo from github for the builder.
I do not see anything here related to git+freebsd.
No it's intentional but it's not controlled in the source by the sysctl, but the "conscontrol mute [on|off]" command, notably it's run in /etc/rc and other places via the mute_kernel_msgs() / unmute_kernel_msgs() function in /etc/inc/util.inc