Yep, it's a straight-through port. Just plug the A3000's video out into the Picasso's second port.
As to original equipment, I believe the card shipped with a very short VGA cable (to minimize clutter) for just such a connection. Amigas with only the 23pin ports still had to use the Commodore VGA adaptor. I suppose a custom 23->15pin cable would also work.
