Care to explain why they would say on the one hand, we don't want to release the scores because it isn't relevant in determining discrimination, then on the other, your study can't show discrimination because it isn't taking into account the credit scores? I am having a hard time vesting these institutions with any credibility whatsoever when they play these kinds of games.
If their criteria truly are race neutral as you claim, then analyzing the full data set will allow us to control for all other variables in the application process to determine if race can or cannot be isolated as a determinative variable in and of itself. If banks are denying loans to blacks with the same income, assets, credit scores etc. as white applicants who are being approved, then "disparate impact results" aren't relevant here because discrimination is happening at the front end based on race. If not, then not. Either way, we need the full data set for proper analysis. If it proves no discrimination, the banks should be willing to release it as it will only exonerate them. OTOH, it could only be used "against them" as you say if the credit scores fill in the final piece of a puzzle which proves racial discrimination.