I don´t think he is good for 9 Tails cause his mystery doesn´t deal dmg. a ninja with a passive barrier like Darui would be much better.
Tho if you are only running for 3 rounds every time, he might be good.

Yeah he can be good since unlike other ninjas with barrier like Sasuke, Gaara, Haku, and Anko, his mystery won't deactivate the barrier if you're on auto (Although it won't do damage). Also, you can pretty much put him anywhere on your ninetails team without having to put him in first spot since Danzo sets his barrier up instantly. Only problem with Danzo in ninetails, I think, would be that he'll try to chaos ninetails every round, which doesn't do damage; just waste time which adds up over time.