How do I mark a contact as VIP if that contact does not have an email address?

So... I have my phone set to go into Do Not Disturb at 9PM. I have the key contacts from my clients marked as VIP so they will always get through to me. However, I also have environmental monitors in several server rooms that will call me with alerts (temperature, loud noise, etc). So these contacts (the monitors) have valid phone numbers as these devices place an actual voice call. However, they do not have an email address. I'd like to flag them in my Contacts list as VIP so calls from them will also go through when my phone is in DND. Is there a way to do this without using the email app?