Comment 3 for bug 1562387

However, I was able to get progress on this issue: now xsetwacom works. What was happening is that the first dbus entry for evdev had a catchall rule for tablets which assigned evdev drivers to the tablet before the wacom drivers would have a chance.

So I editted:
/usr/share/X11/xorg.conf.d/10-evdev.conf

and commented the catchall tablet rules and then added
/usr/share/X11/xorg.conf.d/50-huion.conf

With these contents:
# Huion tablets
Section "InputClass"
    Identifier "Huion class"
    MatchProduct "HUION"
    MatchIsTablet "on"
    MatchDevicePath "/dev/input/event*"
    Driver "wacom"
EndSection

Section "InputClass"
    Identifier "Huion buttons"
    MatchProduct "HUION"
    MatchIsKeyboard "on"
    MatchDevicePath "/dev/input/event*"
    Driver "evdev"
EndSection

Section "InputClass"
    Identifier "Huion scroll"
    MatchProduct "HUION"
    MatchIsPointer "off"
    MatchIsKeyboard "off"
    MatchIsTouchpad "off"
    MatchIsTablet "off"
    MatchIsTouchscreen "off"
    MatchDevicePath "/dev/input/event*"
    Driver "evdev"
EndSection

And now the tablet is recognized by xsetwacom:
[17:31] [4961] [patola@trololo patola]% xsetwacom --list
HUION PenTablet Pen stylus id: 10 type: STYLUS
HUION PenTablet Pad pad id: 11 type: PAD

However, the System Settings Wacom entry still does not recognize it, "No tablet detected". I guess I will have to do it manually in the meanwhile?

BTW, this is issue #26 from digimend drivers: https://github.com/DIGImend/digimend-kernel-drivers/issues/26

So there IS a bug to be fixed in xserver-xorg-core: /usr/share/X11/xorg.conf.d/10-evdev.conf and huion configuration.