Can you search using an index while indexes are being updated in oracle11g?
Here is what the 11.2 Concepts Guide says about doing selects while dml is changing an index (ephasis mine):


  The database automatically maintains and uses indexes after they are
  created. The database also automatically reflects changes to data,
  such as adding, updating, and deleting rows, in all relevant indexes
  with no additional actions required by users. Retrieval performance of
  indexed data remains almost constant, even as rows are inserted.
  However, the presence of many indexes on a table degrades DML
  performance because the database must also update the indexes.


So, you might see sightly degraded performance if you have a lot of indexes and a lot of DML taking place, but I suspect this is insufficient to cause the appearance of hanging.  I suggest you trace a session to see what is slowing the search down.