I finally made it to Act III with a completely new character, started post patch 5. In my old Minthara run Withers refused to acknowledge the relationship properly, this time around he actually does. Previously I only had it work with the Drow Twins.
However there sadly still is no different greeting from Minthara, nor a kiss option - which was to be expected. I'll see if I get the "special word dialogue" with her at some point with this, at least.
