how to search for contacts selected in contact reference fields
Lack of searchability is one of the downsides to using Contact References.

1) One option is to use Relationships instead of Contact Refs.  You can create a smart group based on those - but you would need to convert your existing Contact Refs and associated processes.

2) Jaap's DataProcessor extension can help. 


Add a Data Source of type Individual - call it Person
Add a second Data Source of type Individual - call it DC.  


Join type as 'Select fields to join on'
Join on Field: Contact ID = Person::custom group::DC contact ref

Add fields for the fields you want to display for Person and/or DC using 'Raw field value' - include the DC contact id.
Add an Output of Contact Search


That will search for contacts who are DC's and show the fields you configure.

Although Contact Search has an action to create a smart group, I have not got that to work with DataProcessor (yet) - so it does not completely solve your problem.  You could though run it and add the found contacts to a static group.

I guess Jaap would welcome any PR's or sponsorship to make smart groups work as a dataprocessor output.