I think they would, but in a very subtle way! Like matching patterns or complimentary colors. Luffy would probably be happy to go all the way with it, but Law thinks it's embarrassing to parade around in perfectly matching outfits. It's basically announcing they're together, and Law is shy.

Maybe they start influencing each other's styles in small ways though. Like Law wearing red clothes because the color reminds him of Luffy, or Luffy getting heart-themed accesories.