OK this is interesting! I see that when I add a product through the Product Admin in the CMS the has_one relationship is established! Somehow, I do not have the method right on my front end form.....any ideas? The form looks like this:

Thank you Will, that solution indeed works perfectly. Thanks for taking the time to respond. SilverStripe is awesome, I also want to thank you and your team for making this superb CMS and framework. I heavily evaluated over 10 CMS before I started using SilverStripe and nothing compares. I am always delighted what I can build using the framework, nothing else is this flexible. Part of me wants the whole world to know about it, and part of me wants to keep it my own little secret weapon ;0) HA!

This is working great, but could you tell me if it would be possible to associate the DataObject with a group instead of an individual member ID, so that members of the group can edit and create the products?

Provided you have the relationship setup on your Product

public static $has_one = array(
'Editors' => 'Group'
);

Then you can assign to that group by doing a search for that group

$group = DataObject::get('Group', "Code = 'some-group-name'");
if($group) {
$product->GroupID = $group->ID;
$product->write();
}

You could also include code to create the group if needed

if(!$group) {
$group = new Group();
$group->Code = 'some-group-name';
$group->Title = "Some group";
$group->write();

$product->GroupID = $group->ID;
$product->write();
}