Since drop table is a DDL statement that:
1. can't be part of a transaction and
2. can't be undone
I would say it's highly unlikely that it uses the undo log for anything.
There are some interesting reading in the manual for the related statement TRUNCATE TABLE (which basically is like a DROP TABLE; CREATE TABLE combination) and hence is not related to normal DML statements that can be part of a transaction and in need of the undo log.
Do you know what happens under the covers when a table is dropped?
1) A bunch a DELETE commands, thus involving the undo log and possible purge lag?
2) Write over the former table's extents with some default value?
3) Just mark the extents as reusable without cleaning them up?