Yahoo Mail App - Send Email To Contact List
Okay, I just figured out a workaround. You can export your Yahoo Contact Lists by:


Signing into your Yahoo Account via their web interface,
Clicking on the "Contacts" icon, and
Choosing "Actions" => "Export".


This will create a CSV file which can then be used to import the contacts into a Gmail account via Google's web interface. After that, you can sync your Gmail contacts to your phone using the Android Gmail app. This will create the contact lists from Yahoo and import them into your phone as contact groups on the device.