I add wine yeast to my sours when I bottle. I've had some early sours not carbonate well when I did not re-yeast. Maybe I was doing something wrong, but I've never had a carbonation problem since I started reyeasting. I use dry wine yeast and just tap a few cells into the bottle before corking or capping.
Maybe it all depends on how much viable brett is left in solution (just like bottle conditioning clean beers). Length of conditioning, strain, initial pitch rate, acidity levels, etc. etc. Maybe I'm just getting lucky w/ bottles. I have had kegs of funky beer not carb on their own...
Pitching new yeast is definitely more predictable and shortens carbonating time. I just hate to lose so much beer to the thick layer of sediment, and I especially hate getting that sediment in the glass. I like 12 oz bottles or 375 mL, where sediment is a bigger issue than 750mL.
Also, at the 2011 NHC, Chad Y mentioned that large amount of sacch in the bottle gives off a precursor (capric acid?) that brett turns into goaty aromas.
On a commercial time frame, I would be much more inclined to re-yeast (especially if I had better control of pitch rate).
Maybe next time I bottle, I'll try pitching a bit of fresh brett?