Hi Jiten..
Service Tax shall be applicable even on reimbursement of expenses which is charged along with the actual consideration. Pls refer Rule 5 of the Service Tax (Determination of Value) Rules 2006.
Rule 5 -
5. Inclusion in or exclusion from value of certain expenditure or costs.-
(1) Where any expenditure or costs are incurred by the service provider in the course of providing taxable service, all such expenditure or costs shall be treated as consideration for the taxable service provided or to be provided and shall be included in the value for the purpose of charging service tax on the said service.
Hope this clarifies your doubt. So whether there's a separate bill, or a separate disclosure, according to me, it does not make any difference. Service Tax will be chargeable.