If we don’t provide CE credit for the abstracts, are we allowed to include advertising in the handouts (print or digital) that DO contain abstracts?

The answer depends entirely on what role the handout (with abstracts) plays in the CE activity.  If they are referenced during the activity or play any part in the accredited content itself, then, no, advertising would not be allowed.  If the only activity-related information in the handout is logistical information about the activity, then, yes, it would be allowed.