Dear Mr. Dharmendra,
1. Ans Yes commission paid to overseas agent come under the category of Business Auxilliary Services definition and attract service tax.
But this service will come under Export of service Rule, Rule 3(1)(iii) and u may claim refund as per the rules prescribed.
in the case of Blue Star Ltd v. CCE, (2008 (3) TMI 32 - CESTAT BANGALORE) and some other cases will be applicable in your case.
2. No actually in this case CENVAT Credit not applicable, u may claim the refund only
3. no exemption available, only refund available.