Hi,
1Z0-042 is the DBA track, and the information in the following link
OTN Site for certification suggests that only a working knowledge of Sql is required. However, in my opinion, to be a good Oracle DBA, its best to have a good working knowledge of SQL, PL/SQL too
Hope This Helps
[ August 02, 2007: Message edited by: sriram chandra mouli viswanathan ]