You can probably already do this on Termux, since PiHole doesn't need graphical acceleration.
Might have to create a proper Chroot though, dunno if their Proot tools would have enough privileges for this use case.
You could use Termux for this. However, you won't be able to use containers. You would need to either build it from sources or run it in proot. I also think the DNS settings in Android are limited so you may have trouble getting it to work. You would need pihole to listen on a random available port and then somehow get android to send DNS to that port. So it probably wouldn't work.
However, your welcome to try just make sure you use the F-droid version of Termux.