Can I program intercom calls between intercoms/video intercoms on a system without a separator?

Yes, you can program intercom calls regardless of whether the separator is present or not. Remember that when a call comes from an outdoor station, any intercom conversation is interrupted because of lower priority. The presence of an island (hence a separator) allows intercom calls even if there is a call from the outdoor station to a different intercom/video door entry monitor on the system.