My WAG is that it won't really matter whether you pitch for the first step or the whole volume, as long as you're consistent the beer should also be consistent. It might be worth experimenting. If you can save money pitching less yeast and make the same quality of beer, why not? It might be an expensive experiment, though.
The big problem with stuff like this is that it is usually non-linear in nature. So someone's experiment to prove this has no effect on a 6 gallon batch might not scale to 7 or even 30 bbls. Same thing with gravity, it could be that a beer with a gravity below 12 plato shows no issues but beers above have problems or vice-versa.
Ultimately, on a professional scale, while the yeast pitch is the most expensive component of many batches, unlike the majority of the other inputs, that cost gets split into a fraction as you reuse the yeast in each further generation. And the fact that most breweries are pretty religiously repitching makes an experiment like the above, even more risky, all for saving what will probably amount to $20-40.