Even with deoplete-zsh plugin, command name completion does not work. It seems to that deol is expecting deoplete-zsh to provide bash completion, but deoplete-zsh does not seem to provide it, and I don't think it's an issue in deoplete-zsh since it focuses on zsh, but it's an integration issue in deol-edit.
https://github.com/Shougo/deol.nvim/blob/0c6e1653f0d0a904efa8da01e470ffe0bd1bf594/doc/deol.txt#L56
Even with deoplete-zsh plugin, command name completion does not work. It seems to that deol is expecting deoplete-zsh to provide bash completion, but deoplete-zsh does not seem to provide it, and I don't think it's an issue in deoplete-zsh since it focuses on zsh, but it's an integration issue in deol-edit.