Dealers still use the 633 gaskets rather than the superior 642 or 770 and in general their technician level of competency is rather poor. Subaru and other dealers don't want to spend any more on training than they need to. Monkeys that swap entire assemblies are much easier to train and cheaper to pay than a REAL technician that can diagnose, disassemble intricate parts, and reassemble correctly.
It's absolutely a false sense of security to believe in the superiority of the job just because it's a "dealership". Personally I wouldn't put any more faith in it than a proper independent job especially if no part numbers are listed.
GD