Probably but you won't be able to use anything else in the Docker tab. The code looks to see if the system is i386 or has docker.com in /etc/apt/sources.list.d/omvextras.list and if either is true, it will always check for docker.io. Is there a reason you don't want to use the version in the Debian repos? it is 18.09 which is plenty new to do just about anything.
I am used to making sure that software is always the most up to date version available, but I suppose it wouldn't matter if Docker was a few versions behind the latest so long as there are no critical flaws that need fixing. Using the Debian Docker version would make server admin easier!!
Is there is a relatively easy way to get from one version to the other?
If I uninstall the current version of Docker will all existing containers be removed as well? or will the config be preserved so the Debian Docker version can pickup where the other left off?
The config data is mapped to a folder on the HDD so this would be safe