I agree with DT and TB that there is 0 evidence that Rocco had anything to do with the Tahoe assassins.

However, I disagree with this persistent theory that Neri passed over Rocco. Nothing of the sort happened. Neri was selected by Michael to be Michael's bodyguard, his Luca. In that position, Michael came to trust him and depend on him. He accompanied Michael on his trips including what apparently is his initial foray outside of NY to Las Vegas resulting, in part, in Moe Greene's murder. Rocco came later thru Clemenza and was "only" a capo. Consistent with the Corleone's propensity for a limited number of capos, Rocco receives the attention in that capacity.