AH! Well, you could create fake emails. But then they wouldn't get notices...but it sounds like they might not anyway.
Yea, Moodle does require each account to have an email and usually prevents duplicates BUT I think you can disable that...or create accounts via a bulk upload with the duplicated email--just make sure to change the prevent duplicate emails from yes to no.
If HR doesn't want them to use personal email then they need to make sure they have company emails.