Drupal taxonomy and Civi option groups integration
This is definitely possible.  I've done it to have a custom field store a term id, and user selects from a select list of term names...

You need to implement hook_civicrm_customFieldOptions().
http://wiki.civicrm.org/confluence/display/CRMDOC/hook_civicrm_customFieldOptions

In this provided example below I am using EntityFieldQuery to fetch all terms of the vocabulary with machine name center. 
$fieldID is the custom field id

The custom field with ID 4 in my example was configured as an Alphanumeric data type with a Multi-Select widget, but you could use a regular select widget as well.

I hope this gets you started!

function YOURMODULE_civicrm_customFieldOptions( $fieldID, &amp;$options, $detailedFormat = false ) {
    if($fieldID == 4) {
        $center_query = new EntityFieldQuery();
        $center_query-&gt;entityCondition('entity_type', 'taxonomy_term');
        $center_query-&gt;entityCondition('bundle', 'center');

        $centers_ids = $center_query-&gt;execute();

        $detailed_options = array();

        $centers = entity_load('taxonomy_term', array_keys($centers_ids['taxonomy_term']));

        foreach($centers as $center) {
          $label = '';

          $label .= ' ' . $center-&gt;name;
          if($detailedFormat) {
            $detailed_options[$center-&gt;tid] = array (
              'id' =&gt; $center-&gt;tid,
              'value' =&gt; $center-&gt;tid,
              'label' =&gt; $label,
            );
          }
          else {
            $options[$center-&gt;tid] = $label;
          }

        }

        if($detailedFormat) {
          $options += $detailed_options;
        }

        asort($options);
      }
}