I recently got an Odroid-XU4 to test with HackRF and GNU Radio Companion and remembered this posting.
After having flashed SD and booted the Armbian distro, I dont see any problems installing Pi-hole on Armbian:
Static hostname: odroidxu4
Icon name: computer
Operating System: Debian GNU/Linux 9 (stretch)
Kernel: Linux 4.14.94-odroidxu4
Its a Debian derivative using the official Debian repos plus some Armbian specific repo’s:
$ sudo grep -v '^#\|^$' -R /etc/apt/sources.list*
/etc/apt/sources.list:deb http://httpredir.debian.org/debian stretch main contrib non-free
/etc/apt/sources.list:deb http://httpredir.debian.org/debian stretch-updates main contrib non-free
/etc/apt/sources.list:deb http://httpredir.debian.org/debian stretch-backports main contrib non-free
/etc/apt/sources.list:deb http://security.debian.org/ stretch/updates main contrib non-free
/etc/apt/sources.list.d/armbian.list:deb http://apt.armbian.com stretch main stretch-utils stretch-desktop
And I believe architecture is a supported one:
Not sure which image works for Odroid-U3 but you could try the Odroid-XU4 “Armbian Stretch” one as HW is similar:
Have you tried installing Pi-hole already via the recommended install method ?
EDIT: Ps. I wont be installing Pi-hole on the Odroid because its not mine.