That's kind of a tricky question..And it all depends on how the payment arrangements that you have set up with the dropshipper...If you are selling the product and the customers pay you and then you pay the dropshipper, then you using paypal should be no problem..If the customer pays the dropshipper and then the dropshipper pays you your cut, then you will need to find some other sort of payment arrangement more suitable to your customers..
I can tell you that if your customers are sending the money to the dropshipper, then you should probably find another dropshipper, as most customers are going to shy away from someone who only accepts wire transfers and you should too...
Most dropshippers who are legit that I know of receive payment from you, ( the seller) for the products that you sell, and the customer sends the payment to you, you take your cut and send actual payment to your dropshipper for whatever he is selling the product to you for...
I myself would not be doing business with any dropshipper who only takes western union or wire transfer for payment. If something goes wrong, you'll be left hanging in the wind...