I hacked the uc_inventory_api.module to be compatible with Gift Certificates by adding the final 'and' condition on line 187:

if(isset($form['attributes']) and count(element_children($form['attributes'])) and !array_search("Recipient's Email Address", $form['attributes']) ) // do we have attributes on this product?

Replace "recipient's email address" with the name of your attribute to use the module again.

Also, confirmed that inventory/simple stock module does not prevent users from adding more items than is in stock via the quantity field in the shopping cart.

Cheers,

Shiraz