I'd made a similar deck for Towers Standard, but it looks like I ended up deleting it. Competitive? Perhaps. My deck used 4
Black Traitor and 2-3 Grima as the only Isengard minions. The biggest benefit for using Saruman is that you don't have to run the risk of letting him die in a skirmish. Even with
Wizard's Device equipped, I often chose not to have him skirmish so that I'd have a minion to spot for
News of Mordor and
Men Will Fall. While Grima is often overwhelmed, sometimes he'll be tossed onto the ringbearer or Legolas and survive the skirmish. For each of them, the only real function was to aid the events for Nazgul. I had the idea to play
Master of Foul Folk and pull
Banner of Isengard for free onto Grima for survival, but decided it was too convoluted for a minion who will still die to any Rohan companion.
In TS, the biggest pitfalls were the strength of Rohan and the twilight required to play everything you'd like - especially against
Dauntless Hunter. I ran far fewer Isengard minions, so I had to save up copies of Saruman or Grima with the events and still try to find a Nazgul to play, and then find the twilight to drop everything I needed to, usually at least 9: 6 for a strong Nazgul, 2 for Grima, and 1 for the event.
That said, it's a lot of fun to suddenly overwhelm Gimli or watch Eomer die at site 5 unexpectedly from the damage. Grima helps keep
Armor away, but it's no use against ring-bound rangers. If I were to remake it, I'd build a bigger deck with a fellowship which can cycle heavily, and perhaps splashing
They Are Coming with 4 Moria Scouts for cycling and twilight.
Now your deck takes the opposite approach from mine - splashing Nazgul with Isengard. I agree that
Black Breath isn't going to be all you want it to be, especially since you'll have relatively few chances to put it on the companions you'd like to.
Agents of Orthanc, I fear, will always be worse than having a good Nazgul, but again your focus is opposite of what I had so I don't know how it plays. Lemenya has potential, but you probably won't be able to play 2 Nazgul and a Man and have enough leftover for an event. Someone else once said he's redundant: if the -2 strength is enough to keep them from competing with a 9 strength minion, you're already winning and you could've played another minion. If not, you need another minion so you can gain the upper hand. He's too easily eliminated or tolerated, and you're already playing long odds with a hybrid deck without also trying to work him in.
I really like
Desertion, though. Instead of
Black Breath, what about
Wounded? Another condition for
Rohirrim Traitor to spot, better effect, and the decks without Men are the ones Nazgul tend to do the best against. Also remember that it can be played on Barliman when facing off against Gandalf!