because you can have multiple users of a CI you I don't think that you can target the User email addresses directly from a rule. However an approach you can take is to target the owner or administrator of the CI for mail notification.
Also do you want users notified all the time of issues with a CI especially wher you have redundancy betweeb devices. In this case there may be no impact visible to users when one CI goes down so should they be notified? There would be a need to notify the owner / administrator though.