Can a non devil fruit user use Haki with Seastone cuffs? This question is basically an extension of this question, in which it's mentioned that a devil fruit user can't use Haki because he/she gets weak due to seastone, but seastone shouldn't have any affect on Non-Devil fruit user.  So can they use Haki while they are in contact of seastone? Like Zoro and Ussop did during Water 7 arc.
Yes, they can. There isn't very direct proof though, but the much we have, it says, no dfs are fine and can use haki. Although I am not use about breaking them using haki... Seastones are very durable. Probably it required advanced haki to break them!!