Erm, I’ve just realized that simply disabling said systemd service unit, if it exits, should do. So I installed the package to be able to grep in its contents and found that there is one caller that can’t be overridden as it seems: /usr/lib/systemd/system-sleep/nvidia; there is no override mechanism for that, at least none that I know of. It looks like dpkg-divert it is then. 
sudo dpkg-divert --local --no-rename /usr/bin/nvidia-sleep.sh
That should do it. From now on package upgrades will divert that file to /usr/bin/nvidia-sleep.sh.distrib and not clobber your local edit. Since that script will exit 0 right away, you could even do this:
cd /usr/bin && sudo ln -sf true nvidia-sleep.sh
Shave off some CPU cycles by not having to spawn a shell which immediately exits. 
That will destroy the file, however, so, if you intend to keep the original, change the the above command to:
sudo dpkg-divert --local --rename /usr/bin/nvidia-sleep.sh
That way you will have a backup of the packaged version. But then you have to create the symbolic link, because callers of that script will get a no such file error.
On a more ranty note, I’m underwhelmed by the quality of the package contents, because this happened during installation:
Created symlink /etc/systemd/system/systemd-hibernate.service.wants/nvidia-hibernate.service → /usr/lib/systemd/system/nvidia-hibernate.service.
Created symlink /etc/systemd/system/systemd-suspend.service.wants/nvidia-resume.service → /usr/lib/systemd/system/nvidia-resume.service.
Created symlink /etc/systemd/system/systemd-hibernate.service.wants/nvidia-resume.service → /usr/lib/systemd/system/nvidia-resume.service.
Created symlink /etc/systemd/system/systemd-suspend-then-hibernate.service.wants/nvidia-resume.service → /usr/lib/systemd/system/nvidia-resume.service.
Created symlink /etc/systemd/system/systemd-suspend.service.wants/nvidia-suspend.service → /usr/lib/systemd/system/nvidia-suspend.service.

There are three WantedBy= directives in nvidia-resume, for instance:
# /usr/lib/systemd/system/nvidia-resume.service
[Install]
WantedBy=systemd-suspend.service
WantedBy=systemd-hibernate.service
WantedBy=systemd-suspend-then-hibernate.service
The proper way of running services at suspend/hibernate/resume is to just have the sleep.target special target depend on them, so this is equivalent and less ugly:
# /etc/systemd/system/nvidia-resume.service.d/override.conf
[Unit]
After=sleep.target
[Install]
WantedBy=
WantedBy=sleep.target
(that’s a working override, BTW, can put it in the location in the comment and then run systemctl reenable nvidia-resume after the obligatory systemctl daemon-reload)
I can only hope that Canonical is just repackaging NVIDIA’s slop here, because that’s a look under the hood I’d rather not have taken. 
Plus, these services make /usr/lib/systemd/system-sleep/nvidia utterly redundant! This is what the official systemd docs say:
Note that scripts or binaries dropped in /usr/lib/systemd/system-sleep/ are intended for local use only and should be considered hacks.