Actually, it looks like Hyprland does call dbus-update-activation-environment, it just does not include PATH and XDG_DATA_DIRS, which are necessary for application launchers and file associations.
There is an upstream issue about that: Import environment variables into systemd in NixOS modules · Issue #2800 · hyprwm/Hyprland · GitHub Also Xwayland applications don't startup when launching them from `nautilus` · Issue #2965 · hyprwm/Hyprland · GitHub