I believe that it's safe to uninstall oem-somerville-three-eyed-raven-meta after the upgrade. This will uninstall various other packages, but none of them should be required since the standard 22.04 packages include support for all the hardware. The long justification for this follows.

I did some digging into what I had installed from that repository and what those packages contained. Firstly:

$ dpkg -l 'oem*'|grep '^i'

ii  oem-somerville-meta                  22.04ubuntu2 all          hardware support for Somerville project

ii  oem-somerville-three-eyed-raven-meta 20.04ubuntu4 all          hardware support for Somerville Three-Eyed-Raven platform

It appears that I originally had oem-somerville-three-eyed-raven-meta installed for Focal, it gained a dependency on oem-somerville-meta in May 2020, so that got installed at that point.

The oem-somerville-three-eyed-raven-meta package contains /etc/apt/sources.list.d/oem-somerville-three-eyed-raven-meta.list with contents

deb http://dell.archive.canonical.com/ focal somerville

# deb-src http://dell.archive.canonical.com/ focal somerville

deb http://dell.archive.canonical.com/ focal somerville-three-eyed-raven

# deb-src http://dell.archive.canonical.com/ focal somerville-three-eyed-raven

The upgrade to 22.04 changed the file in my filesystem to contain:

deb http://dell.archive.canonical.com/ jammy somerville

# deb-src http://dell.archive.canonical.com/ focal somerville

#deb http://dell.archive.canonical.com/ jammy somerville-three-eyed-raven

# deb-src http://dell.archive.canonical.com/ focal somerville-three-eyed-raven

and of course there's no http://dell.archive.canonical.com/dists/jammy-somerville-three-eyed-raven/ directory.

The oem-somerville-three-eyed-raven-meta_20.04ubuntu4_all.deb package contains:

drwxr-xr-x root/root         0 2020-05-12 09:41 ./

drwxr-xr-x root/root         0 2020-05-12 09:41 ./etc/

drwxr-xr-x root/root         0 2020-05-12 09:41 ./etc/apt/

drwxr-xr-x root/root         0 2020-05-12 09:41 ./etc/apt/sources.list.d/

-rw-r--r-- root/root       270 2020-05-12 09:41 ./etc/apt/sources.list.d/oem-somerville-three-eyed-raven-meta.list

drwxr-xr-x root/root         0 2020-05-12 09:41 ./usr/

drwxr-xr-x root/root         0 2020-05-12 09:41 ./usr/share/

drwxr-xr-x root/root         0 2020-05-12 09:41 ./usr/share/doc/

drwxr-xr-x root/root         0 2020-05-12 09:41 ./usr/share/doc/oem-somerville-three-eyed-raven-meta/

-rw-r--r-- root/root       455 2020-05-12 09:41 ./usr/share/doc/oem-somerville-three-eyed-raven-meta/changelog.gz

-rw-r--r-- root/root      1037 2020-05-12 09:41 ./usr/share/doc/oem-somerville-three-eyed-raven-meta/copyright

The /etc/apt/sources.list.d/oem-somerville-three-eyed-raven-meta.list file is the only one with any real effect.

The oem-somerville-meta_22.04ubuntu2_all.deb file contains:

drwxr-xr-x root/root         0 2022-04-26 13:01 ./

drwxr-xr-x root/root         0 2022-04-26 13:01 ./usr/

drwxr-xr-x root/root         0 2022-04-26 13:01 ./usr/share/

drwxr-xr-x root/root         0 2022-04-26 13:01 ./usr/share/doc/

drwxr-xr-x root/root         0 2022-04-26 13:01 ./usr/share/doc/oem-somerville-meta/

-rw-r--r-- root/root       245 2022-04-26 13:01 ./usr/share/doc/oem-somerville-meta/changelog.gz

-rw-r--r-- root/root      1012 2022-04-26 13:01 ./usr/share/doc/oem-somerville-meta/copyright

drwxr-xr-x root/root         0 2022-04-26 13:01 ./usr/share/glib-2.0/

drwxr-xr-x root/root         0 2022-04-26 13:01 ./usr/share/glib-2.0/schemas/

-rw-r--r-- root/root       326 2022-04-26 13:01 ./usr/share/glib-2.0/schemas/15_oem-somerville-meta.gschema.override

and the only file there with any effect is 15_oem-somerville-meta.gschema.override which contains:

[org.gnome.shell]

favorite-apps = ['ubuntu-desktop-installer_ubuntu-desktop-installer.desktop', 'ubiquity.desktop', 'firefox_firefox.desktop', 'google-chrome.desktop', 'thunderbird.desktop', 'org.gnome.Nautilus.desktop', 'rhythmbox.desktop', 'libreoffice-writer.desktop', 'snap-store_ubuntu-software.desktop', 'yelp.desktop']

which (I assume) populates the initial set of favourite applications for Gnome shell.

So, for anyone that doesn't care about that initial set of favourite applications (which is probably almost everyone) the only benefit of having these packages installed is their dependencies. For oem-somerville-meta these are dconf-gsettings-backend | gsettings-backend, ubuntu-oem-keyring and for oem-somerville-three-eyed-raven-meta these are ubuntu-oem-keyring, linux-generic-hwe-20.04, oem-somerville-meta. That dependency on linux-generic-hwe-20.04 in turn means a dependency on linux-generic-hwe-22.04. (There isn't currently a newer hardware-enablement kernel available for 22.04.)

I think this means that it's safe to uninstall oem-somerville-meta, oem-somerville-three-eyed-raven-meta. Doing this means that apt autoremove will also remove linux-generic-hwe-20.04, linux-generic-hwe-22.04, linux-headers-generic-hwe-22.04, linux-image-generic-hwe-22.04 and ubuntu-oem-keyring. Removing all of those packages hasn't caused me any problems so far.