can't help with the openrc stuff but i looked at /etc/init.d/udev and on my install, devuan excalibur+sysvinit, this service is non-functional so deleting it would not change anything.

the udev daemon is not active:

/home/xyz> service udev status

this is due to the udev script exit'ing at the earliest possible moment:

/home/xyz> grep DAEMON /etc/init.d/udev
DAEMON="/lib/systemd/systemd-udevd"
[ -x $DAEMON ] || exit 0

on this machine, this is what i find in /lib/systemd

/home/xyz> ls -l /lib/systemd/
total 30
drwxr-xr-x 2 root root 3452 Mar 14 15:45 ntp-units.d
drwxr-xr-x 4 root root 8192 May 30 12:59 system
drwxr-xr-x 2 root root 3452 May 27 23:44 system-generators
drwxr-xr-x 2 root root 3452 May 27 23:44 system-preset
drwxr-xr-x 2 root root 3452 Dec 23 15:54 system-sleep
drwxr-xr-x 8 root root 8192 May 16 19:59 user

i have no idea why the udev service file exists. the eudev service file is largely identical and is active. the udev service file must be a relic from devuan's past?

a quick search of the gentoo forums mentions that this openrc error message is due to "duplicate services", so  maybe there are  different services using the same name? check your system and spend some time searching the gentoo forums, there may be threads similar to your issue there.

Error: udev is the name of a real and virtual service.

That appear at init:

I have found this post:

https://dev1galaxy.org/viewtopic.php?id=7766

Where it say that an user has solved deleting the udev service in /etc/init.d.

I have done a little search with dpkg and found that:

sudo dpkg -S /etc/init.d/udev
initscripts: /etc/init.d/udev

sudo dpkg -S /etc/init.d/eudev
eudev: /etc/init.d/eudev

What is a correct way to address this problem?

I'm using OpenRC and

PRETTY_NAME="Devuan GNU/Linux 6 (excalibur)"
NAME="Devuan GNU/Linux"
VERSION_ID="6"
VERSION="6 (excalibur)"
VERSION_CODENAME="excalibur"
ID=devuan
ID_LIKE=debian
HOME_URL="https://www.devuan.org/"
SUPPORT_URL="https://devuan.org/os/community"
BUG_REPORT_URL="https://bugs.devuan.org/"

Kind regards
Carlo D.