That would depend on the packagers of that repository. Then there's
RPMFind, RPMForge, and bazillions (bajillions, even!) of others out
there as well. There's a very high probability that folks end up with
PHP5.3 on their servers when doing routine updates.
If PHP5.3 breaks any compatibility with 5.2, it should have been
called something else, but that's water under the bridge at this
point.
-- Mitch