Try this:
$conditions = array(
'or' => array (
array( 'and' => array( 'Claim.company_id' => $companyId, 'Claim.id' => $claimNumber )),
array( 'and' => array( 'Claimant.first_name' => $claimantFirstName, 'Claimant.last_name' => $claimantLastName ))
)
);
$this->ModelName->find('count', array( 'conditions' => $conditions ));