For a professional there should be no difference in setting up a righty or a lefty. What I don't like in the setups offered by most specialists is that they will follow the book, so to speak, measuring distances and gaps and making them all standard according to "the rules". I don't know how many of us enjoy standard setups, but I know I certainly don't: for instance, I like the G string to have a much lower action than the other strings (makes it easier to play the high notes when I use my pinky). I like to adjust the action through lifting or lowering the saddles and the nut (Warwicks are way ahead of most other makes, in that they have adjustable ones) as well as through the usual truss rod tweaks. Some of the above would be anathema to a pro...
I'm the official re-string/setup person in our lefty+righty household, and it makes no difference to how I work; however, I always do the final adjustments only after we have actually played the bass and decided if it still needs tweaking.