So, in theory, you shouldn't make a starter with this yeast then? I repitched from a friend's slurry and gave him my slurry and our sours were great. Different, yes, but since the yeast kicks in first, the lacto and pedio follow and the Brett takes what is left, it still worked out well with an extended aging period.
That's one school of thought, and I've made a few good Flanders Reds by just dumping in 2 packs.
You've gotta watch the dates on Roselare - it doesn't turn over in the LHBS like 1056. If its older, supplement with more packs or some additional sacch cells (starter, slurry, partial pack of dry yeast).
Cell count/health is important in all fermentations, including sours. Higher alcohols and phenols produced from poor fermentation conditions (no temp control, low cell count) won't 'age out'.
I believe you can make a starter with Roselare with no ill-effects. Sacch will outcompete brett and bacteria in a aerobic, low gravity, all-malt wort, but all the bugs will carry over.
If you're still worried about it, you could make a starter of 3522 or 1214 and pitch it along with the Roselare pack in primary. This is nice if you want a little more character from your sacch. strain.
True, but different doesn't necessarily mean worse, so that's no reason not to try it.
As far as harvesting sours go, I'd argue that those are actually the types of beers where the dregs are harvested the most by homebrewers. I haven't used Roselaire yet, but I've harvested bugs from quite a few commercial sours. If you like brewing sours, then harvesting dregs is an important skill to learn.
Kyle has a great post on his blog on how to wake up your bottle dregs.
Got someone else drinkin' the (sour) Koolaid!