I ran into information from many places about how to install docker and portainer in omv for use.
At least two instances I ran into told me I could "share" the docker folder via smb or nfs so I could see and modify the files via gui if need be.
Well, save yourself the headaches and manage it all via ssh if you can.
I specified my docker directory, installed docker, then portainer then could not get pihole to just start without issue. It kept complaining about various permissions (*.log permission denied, sudoers.so blah blah, etc.). It was a nightmare.
I uninstalled portainer and docker and then deleted the original shared folder I created for docker.
Then I specified a new directory for my docker files under the docker storage area and let docker create it for me. Then I installed portainer and proceeded to install pihole on the first try with no issues.
I think it should be noted that it would be better to just not share your docker folder via smb/nfs like some other sources I ran into suggested.
Also, I didn't need to change port 80 on omv or pihole. I am using my ddwrt router for my dhcp server even with pihole active. I created a macvlan with the proper IPv4 information and my pihole responds on its own IP different from my omv. So typing in omv/ in my browser takes me to the omv web gui on port 80 and typing in pihole/ takes me to my pihole web gui on port 80 as well.
This is my first go-ahead with docker so I am glad I was able to figure it out to this point.