Hi Osman,
Toad does not use DBMS_SQL to parse the SQL. We do, however, use an OCI "Describe" command (as documented here) before query execution to learn the datatypes, but I don't know what Oracle does with that behind the scenes (I doubt it's dbms_sql, but that's up to the Oracle server, not Toad). We perform this "Describe" command in order to determine an ideal number of rows per fetch, and to check for XMLTYPE and CLOB columns. If these are present, we have to get some info about the table incase you later want to edit these columns.
I'm sorry, there is no way to disable the OCI Describe call that Toad makes.
-John