Perhaps. It seems like there's a difference between their regeneration and Marco's. Coc in general is the greatest attack amplifier so it could be a strong enough attack, rather than needing to be coated in Conqueror's in particular.
Holy Knights/Gorosei regenerate slower the stronger the attack but Marco regens instantly no matter the attack.
But HK healing are tied to IMU and never runs out, whereas Marco's might be instant, but doesn't fully heal if he's low on stamina.