I think so, one life for another seems fair, which luffy is more valuable? Yes, it's the captain, if Kuma accepted the deal with Zoro, who is the same as a subordinate, he would do the same with Sanji, who is also a subordinate.
here the goals of zoro or sanji do not matter, both are subordinates, and if kuma accepted zoro, he would do the same with sanji.
P.S; sanji would resist luffy's pain, just like zoro did.