By default, evil-magit uses evil-next-visual-line and evil-previous-visual-line for movement, which is what I want, but for some reason this seems to conflict with enabling evil-respect-visual-line-mode. In my init.el, I have the following use-package declaration for evil:

(use-package evil
  :straight t
  :demand t
  :init
  ;; set before evil is loaded, as per evil docs
  (setq evil-respect-visual-line-mode t))

Normally, this configuration works, e.g. in a markdown buffer with visual-line-mode enabled. However, line-wise movement in magit-mode (e.g. an expanded diff) with visual-line-mode jumps between hard line breaks, as if evil-respect-visual-line-mode was never enabled. If I invoke M-x evil-next-visual-line it works fine, and tells me (incorrectly) that I can run it with 'j'. If I ask for what 'j' does run with M-x describe-key it says evil-next-line.
If I don't enable evil-respect-visual-line-mode then everything works as I would like, and line-wise movement properly accounts for visual-line-mode. Unfortunately, since evil-respect-visual-line-mode has to be set before evil is loaded, I can't disable it for magit-mode only. It's either globally enabled or disabled.