There is no simple correlation between memory and shame. Any time an affect is strongly present, memory is likely to be increased. Think how many people can describe "my most embarrassing moment" and speak of something that occured years before as it were yesterday. It is true that because shame is so cognitively disorganizing, memory of some smaller facts might be decreased in its presence.
If we go back to the basics of affects as described by Tomkins, it is apparent that memory is not really necessary for the triggering of shame. Anytime an impediment to one of the positive affects is experienced, shame will be triggered. Poor memory would be just as likely to be a trigger for shame, as in, "I feel so stupid that I am unable to remember what I should be able to."
What many describe as the apparent decreased amount of shame in some patients with ADD is simply the result of some clinicians being stuck in the paradigm of looking for shame to appear like embarrassment. Please see discussions on the Compass of Shame to get some understanding of how the anger of the patient with ADD may represent the Attack other pole, and the distractability may represent Avoidance.
Your question on the relationship of memory and shame is quite interesting, and I also await Dr. Nathanson's thoughts on this subject.