Plugin eager loading not loading relations
What strikes me as interesting here is your dump contains a Model instance.

For example you said:


  When I dump the response from the service method i'm getting back is:
  Craft\Placid_ResourceModel Object


When I query findAll through a CActiveRecord derived class I get an array of Records. In order to populate this into models, the populateModel(s) methods are typically used.

If you have a relation at the ActiveRecord level, it is a pseudo-attribute and will only be carried through to the model if the attribute is defined as defined attributes can only be mass assigned. Yii also supports rules definitions to mark attributes as safe, but this is almost entirely optional. 

The question is really why you have a model being output.

E.g. for me the following code:

$records = SomePlugin_ProductRecord::model()-&gt;with('pricing')-&gt;findAll($criteria);
var_dump($records[0]);


Results in:

object(Craft\SomePlugin_ProductRecord)#179 (14) {


Do you have any code which is auto inflating into a model? or are you calling populateModel(s)? 

If so, then you have made the correct call of creating the attribute in your model if you want to access it from there, as far as I've experienced.