In order for Zuffa to claim that they DSE defrauded them on the asset sale, it would basically be admitting that Zuffa's due diligence didn't foresee some of the apparent problems in the evaluation of the PRIDE's assets. For example, it was long-rumored that DSE didn't own 100% of the rights to their video footage (Fuji TV produced a lot of the big shows), which may be a possible reason as to why we haven't seen UFC extensively use PRIDE's video library.
Zuffa's reported lawsuit against DSE opens up a major can of worms for a lot of parties and some of the surprises may not be good for UFC in court. Besides the Nevada Gaming Commission having some interest in the lawsuit, you can bet that Ed Fishman will be interested in the proceedings. Additionally, I would expect that some fighters who did not get paid by DSE before PRIDE shut down might consider filing an attachment (lien) on whatever earnings Zuffa gets in the civil suit (think: Miro Mijatovic's lien attachment on the Seiya Kawamata lawsuit against Nippon TV.)
This isn't really my area of expertise, but it's fascinating nonetheless. While the specifics on this matter are few and far between, it would not surprise me in the least to learn Zuffa did not exercise proper due diligence in their purchase of PRIDE. Too many errors were committed in the wake of the purchase for the purchase itself to have been conducted properly. Stay tuned.