Cvets Bethesda Certified SDK uses Fallout.dat
It is not certified, especially by Bethesda, Cvet has used it to his own risk. So it's up to you whether to include it in your client.
Personally I first was paranoid about the inclusion of fallout.dat into the SDK, but now I think it does not really matter. If it comes to problems with Bethesda, it will be more about using Fallout universe and the words "Fallout Online" in the name (that's why it was named "FOnline" long ago).