Would it be possible to make a custom ipsw with a patched function that check the integrity of the iTunesDb file (to always return a success), this would let 3rd party apps to sync with the new 2.x firmware without having to reverse engineer the new iTunesDB hash.

Currently no 3rd party apps are able to sync with 2.0+ firmware, there is an effort here: http://bluwiki.com/go/Ipodhash, but seem like its going to take time, and will need to be re done again when Apple feel like changed the Hash again..