You have a lot of choices when using DTS to import data.  The simplest thing you can do to avoid having to reassign permissions on the destination tables is to just empty the tables before importing the data from Oracle rather than dropping and creating them.  Use an Execute SQL Task with either DELETE FROM or TRUNCATE statements for the two tables.

If, for some reason, you are required to drop and create the destination tables, use an Execute SQL Task with GRANT statements for the two tables.

It is possible to put the logic required to update or insert in a DTS package, especially if the rows can be uniquely identified.  Use either a Data Transformation Task or Execute SQL Task to see if each row exists.