Frozen apps don't matter, removed apps do. Frozen apps are still there to be checked and patched but modified, replaced or removed apps will make an OTA fail.
I never unfreeze apps before an update as re-rooting and granting titanium backup root access again will mark all my previously frozen apps as frozen without having to manually do it.
Freezing an app doesn't touch the app, it tells the OS the app is not available. During the update the OS isn't loaded to even be told the app isn't available and once you do update and boot...the non-rooted OS can't be told those apps are frozen so they are now unfrozen.
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Motorola Droid, Droid 2, Droid 3 and Droid 4 (all rooted)
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