Dramatis Personae clarification

Can Orcs hire Johann the Knife? His description says 'any warband except Skaven, Undead, and the Possessed.

But, Orcs were released after the original books, so...not sure they're meant to have access?

Also curious about whether Orcs can hire Nicodemus. Again, his description says the same as with Johann, but in this case his rules were released in the same 2002 annual as with Orcs.

BTW, Nicodemus seems extremely overpowered for the super-low upkeep of one wyrdstone!

In this day and age its really up to your group.

In my group no, because Skaven, Undead and Possessed were the 'evil' warbands in the basic game.  So he likely would not work for orcs either.  Also note that all the warbands he will work for are human... so maybe he won't sling knives for elfs or dwarfs either.

As for Nicodemus we go with the same rationale. So orcs can't hire him.

Timeline
The orcs appear for the first time in White Dwarf when 'Town Cryer' was a 'free magazine supplement' (Town Cryer #6).  Then they appeared in The Best of Town Cryer and finally in the 2002 Annual.  So they had been out there for 2 incarnations before the 2002.  

Nicodemus originally appeared in 2000 (at least that is when he is included in a scenario called 'An Item Lost" in TC #25 which has a 2000 copyright.)

My point being that GW did not got to any lengths to integrate any new content that they published.  The orc list start showing up in FAQs soon after they are published, but none of the FAQ corrections appear in the 2002 list (for example, including clubs as a weapon choice for orcs and goblins which is ok in every FAQ from 1999 through 2005, but never makes it into the published Da Mob list.)

Also I don't think GW cared what Nicodemus power level was.  They had a model, so they wrote rules for it and sold it.  After that it wasn't their problem.

I figure that Nicodemus was meant more to be used in narrative or Game-mastered campaigns than regular play, so the power level wasn't exactly a problem...

But yes, VK's right that a lot of Mordheim content isn't really integrated, especially given the number of variant settings & timeframes, & additional warbands. Oh, & the sheer number of house rules different groups used, some of which make it into the articles they submitted to Town Cryer -- as I recall, one article blithely mentions 'Fame Points' as if that's something we all know about...

In practise, VK's judgement of saying Nicodemus can't work for 'monstrous' warbands (like skaven, undead, orcs or beastmen) works. I'd say he could also work for (good) elves or dwarves, but not for Witch Hunters or Sisters of Sigmar, on account of him being a filthy witch.

In my group we do not allow orcs & goblins any hired swords due to how large their warband can be (20 warriors!). They just don't need any more models on the table. Granted, animosity does cut back on the effectiveness of these numbers, but at twenty models that's an average of 3 warriors per turn, which still leaves you with 17 functioning fighters (all with a Toughness of at least 4 if you do not use goblins). They are powerful enough as it is.