If it turns out that the "weakness" is actually another type of Haki, and if you believe that Nasjuro blocked Zoro's attack because it would have caused real damage, then that also means Zoro knows how to use that advanced form of Haki or if he shows it against imu army first try without someone telling him
But here's the question who taught Zoro that kind of Haki?
It couldn’t have been Mihawk, since Mihawk only taught him the basics similar to how Rayleigh only taught Luffy the fundamentals. If Mihawk had taught him the advanced stuff, Zoro would probably know future sight by now.
So if Zoro does know this advanced Haki, how did he learn it ?