Perhaps my framing of the situation was a little simplistic. To provide more facts, let me point out that the question of which init system should be default in Debian was first asked[0] to the tech ctte in October of 2013, however it was already clear
the previous month that the GNOME packagers were trying to make systemd the required init system[1] in Debian (which had GNOME as its default graphical environment already):
"Debian GNOME packagers are planning the same AFAIK; they rather just rely on systemd (as init system, not just some dependencies). In the end, the number of distributions not having systemd decreases."
That was written by Olav Vitters, of the GNOME Release Team, who later admitted[2] "Personally I’m totally biased and think the only realistic choice is systemd."
You could argue that any blame for this dependency therefore lies with the Debian packagers, rather than Red Hat employees, but actually, if you look into the history, there was already a push for making GNOME dependent on systemd three years earlier by none other than Lennart Poettering.[3]
Even at that time, Josselin Mouette, founder of the Debian GNOME team, obsequiously replied "I don’t have anything against requiring systemd, since it is definitely the best init system out there currently" and later acknowledged the influence Red Hat had over the direction of GNOME, saying "Red Hat being the company spending the most on GNOME, it is obvious that their employees work on making things work for their distribution" and "on the whole we don’t intend to diverge from the upstream design, on which a lot of good work has been done."[4]
So there was definitely pressure on Debian from GNOME to make systemd the default init, and pressure from Red Hat to make GNOME depend on systemd. Whether or not these decisions were all coordinated in advance in a smoke-filled room is beside the point, given that things worked out exactly the way such a conspiracy would have wanted.
[0] https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=727708#5
[1] https://blogs.gnome.org/ovitters/2013/09/25/gnome-and-logind...
[2] https://blogs.gnome.org/ovitters/2014/02/03/my-thoughts-on-t...
[3] https://mail.gnome.org/archives/desktop-devel-list/2011-May/...
[4] https://raphaelhertzog.com/2012/01/27/people-behind-debian-j...