DJ started more like a Heat power like Oven's, than a Fire power like Ace's.
If he cuts the flames, the leg is still hot as fuck. Would do the same damage if connected.
But that assumes a direct clash, in which case, Zoro's CoA would prevail.
Which means, in this scenario, Sanji would try to dodge the blades in order to get a clean hit. He is faster, have better CoO, so it's completely fine to assume he could do it. Then, if Zoro's couldn't connect with Sanji's kick, his fire cut tech wouldn't mean anything.
Don't think this technique actually changes anything on a fantasy fight between these two.