Modification of user environment in sudoedit was considered a bug and fixed in the 1.8.13 release.
https://bugzilla.sudo.ws/show_bug.cgi?id=688

I'm not sure it's possible to find out if vim is executed by sudoedit anymore. My current workaround is to create a shell function sudoedit() { SUDO_COMMAND="sudoedit $1" command sudoedit "$1" }