I've noticed that OSS, which does not have WB, can take WB mercs like Yuans², McMurrough, Yojimbo ... The problem is, since OSS does not have a WB section, it can only be seen when no type filter is selected. It seems to be similar in other sectorials that are lacking some unit types. Dunno if it's intended or not, but that makes some mercs choices not obvious.
I think you have the Mercs/Soldier of fortune option ticked in settings, those troopers are not normally available to OS.
Sorry my post wasn't explicit enough. Yes i do have that option checked. That's intended if i want to play with soldiers of fortune. The problem is, some troops are not easy to spot because their category does not appear.
I know it's not the best option, but if you order by Type (DES) in the Options menu, you will have the troops that are WD the first in the list. I take note.