Luffy got his skull cracked by sanji but he had no coa?
So yes, he used CoA to crack luffys skull but his CoA was very weak until he fought against Queen. Reminder he got his bone broken by vergo who was capable of the visible CoA.
Sanji has her armament haki since the timeskip. Straight up confirmed by Oda
Some even say he's used it since pre ts cause that's when he used diable jambe. And you need coa to withstand the heat
Sanjis used coa since the timeskip as said by luffy. Was also mentioned twice after. I think he used it in wci and you could see cause of the white pants he had on at the wedding