Limhi seems less concerned about the Lamanites as a threat than the priests of Noah, who are the direct cause of their current level of distress. Finding them and their Lamanite wives would conclusively demonstrate the innocence of the Limhites, thus lessening the anger of their Lamanite guards, even though such a determination would not change the conditions of the original treaty.
As for Limhi’s second cause of concern—raids by the priests—it is not clear how he knows the raiders are the priests and not the Lamanites. If anyone had spotted and identified them, this record does not say so. Logically, the Lamanites have no need to steal, while the priests would be in greater need and would not have had enough time to plant and grow food. Thus, their thievery is understandable.