Update: it appears this problem follows me all over my code - anywhere I use Pair (not just MemberImportProcessor). The problem goes away if I do:
private Pair/*<Member, String>*/ importMember( ... )
Or if I move the definition of Pair inside my EJB JAR (as opposed to packaged in a JAR in my EAR/lib). I believe this further points to a problem in the JBoss scanning process?