For Laravel 5.x only
If checking on main model:
//class_uses retrieves a list of traits from the object passed into an array
//Hence in_array check for name of trait (in string format)
//@param bool $usesSoftDeletes
$usesSoftDeletes = in_array('Illuminate\Database\Eloquent\SoftDeletes', class_uses($model));
If you are checking on the main model's relationship, use the following:
//Replace `myRelationshipName` by the name of the relationship you are checking on.
//getRelated() function fetches the class of the relationship.
//@param bool $relatedUsesSoftDeletes
$relatedModel = $model->myRelationshipName()->getRelated();
$relatedUsesSoftDeletes = in_array('Illuminate\Database\Eloquent\SoftDeletes', class_uses($relatedModel));