There are probably multiple reasons why Apple will use a certain brand at any given time. Price, supply, reliability, etc. While many Mac Pro users were saying the previous brand of OWC's chips (Hynix), were identical to the RAM that shipped in their Macs, mine shipped with Crucial/Micron (at least the 512s I purchased from Crucial looked identical to my Apple-shipped sticks).
It's important to note that the vendor you purchase from is just as important (if not more so), as the brand of RAM you buy. Any vendor's RAM can have problems (including Crucial and Apple), so those vendors who quickly resolve customer issues are highly valuable. In that regard, I wouldn't hesitate to purchase the "untested" (reports from users here), RAM that OWC is now using. (well, I might wait to see a report or two first) 😉
-phil