Given a sufficiently large monitor, it's fine. I (Emacs user) routinely pair with a Vim-using coworker; we just put Emacs on one half of the screen and Vim on the other.

The only thing you need after that is for both editors to automatically refresh when a file changes on disk. With Emacs, you can get that with "(global-auto-revert-mode 1)" in your init.el. You can make Vim auto-refresh too, though I'm not sure how.