Hm, there seems to be a consensus growing amongst the personae in my head that it would be kind of silly to import American tart cherry puree into Belgium. Also, no dried cherries coated with oil. So instead we are thinking of using fresh Belgian cherries: make the base beer, add brett, funk, critters etc., let it do its thing for a year, add fresh cherries in the summer of next year, wait another 3 months or so, then bottle.
If you are after supplication you should try to source dried cherries. The flavor or dried fruit, in my opinion, is very different than that of fresh. but you know as well as I do that a sour beer brewed with fresh tart cherries is fantastic and you would not be dissapointed.
Lot's of folks are fold of the purees but I can offer one reason that whole fruit would be better; the pit. That little stone will add some really interesting flavors especially after a year or more. If RR is using dried cherries they probably don't have the pit so again, if you want supplication keep looking for those dried cherries.
on the oil front, I'm not sure it would be a problem. you are adding the cherries to cold beer. the oil is not going dissolve. it might float on top but that's not a problem if you rack carefully to leave it behind. People add chocolate and nuts to beer all the time and the oil doesn't seem to be a problem. Dry hops area adding oil to cold beer and that doesn't seem to hurt head retention in any way.
so to summarize:
if you want it to be close to supplication use dried cherries If you are not as concerned about that, use local fresh cherries. either way, make sure they are tart cherries because sweet cherries do not have the flavor complexity that I like to see in a cherry beer.