In this situation three stages are involved.
1. You place the purchase order on Nepal supplier. This is export of service from taxable territory.
2. Nepal dealer supplies the goods to a person in USA. This activity is from non-taxable territory to non-taxable territory. Hence no question of GST.
3. Now you receive the amount of profit or commission in the form of foreign exchange. This amount has been received by you on account of export of service (though you have not complied with export procedure) as well as activities happened in non-taxable territories. Services have been enjoyed in a foreign country because of your export of service of placing order on Nepal dealer.
It cannot be denied or challenged.So your profit or commission, whatever you may call, is the result of export of service.
Hence not taxable. Placing the purchase order on a person located outside India is export of service and nobody can challenge it. As a result, foreign currency has been received. Both conditions fulfilled for export purpose or criteria.