Attempting to use :editor/extra-codemirror-options {:keyMap "vim"} does not work in the same way :keyMap "emacs" does. It appears this is due to other keybindings having higher precedence. (The same appears to be true for some emacs keybindings)
See: CodeMirror: Vim bindings demo
The vim CodeMirror keymap appears to have been dropped in version 6, so it might not be more beneficial to upgrade to V6 and implement vim support there directly.
Obsidian has implemented vim support in CodeMirror 6, although it doesn’t appear to be open source anywhere unfortunately. (Though vimrc support is)
There is also this plugin for vim support in CM6: GitHub - replit/codemirror-vim: Vim keybindings for CM6