Let me just be straightforward with my response. The fact is, never go on what a seller promises because the seller just wants to get rid of the property. So call your lawyer who is supposed to be answering this questions and looking out for your best interest and make sure the contract specifically states that the home will be delivered vacant. But here's the other part, if the home is NOT vacant upon closing then you can refuse to go through with the transaction and the contract is void and you get back your down payment. The other option is, if the tenants aren't out by closing then the seler will leave you money in escrow in case you have to take the legal route to evict.
So you have your answer, now make sure you follow through and make your lawyer work for his or her fee. I hope everything goes well and if you need further assistance feel free to email or call.