This is how the company I work for right now does it and it is EXTREMELY inefficient. I've been advocating them to go back to one person to do html/css/js/php.
I can see the above work for large orgs. But with a 3-4 person tech team, super specialization has not worked at all
Designer starts on the project a week ahead of programmer. Gathers requirements (with the programmer tagging along). Does paper sketches which get a general a-ok from everyone.
Does html prototype, ideally already in rails.
Hands off to developer, developer wires up. Over time they iterate together on the same codebase.
Your designer seems to do both (1) and (2) which is more manageable and something I've had work well. Likewise, your programmer seems to do both (3) and (4).
The problems arise when you need to tweak a small feature. You end up needing four-five people(if you count product manager) to touch it to make the change happen. It's not efficient at least for a web start-up(I can see it work for larger enterprises).
That does sound pretty nuts - seems like almost every layout/front-end/design change you'd ever need to make would touch both HTML and CSS, requiring two people to handle it separately.
It works really well. We also continuously try to expand to the others territory.