Thanks for your help but I just took a chance and just changed the OMV port to 81 as its super simple in the web interface and proceeded to installing Pi-Hole. Everything works! The only thing I had to do was to make Pi-Hole the DHCP server because my ISP router (Bell Home Hub 3000) was not playing nice for some reason.... All and all, I installed OMV., Emby and Pi-Hole on my raspberry Pi 4 without using docker and everything is working.
Cheers!
Lex