Do BBs pay signing bonuses / buyout equity and deferred comp at the senior associate level?

I'd say that, like almost anything when it comes to comp (and that's what this is - however you call it, money is fungible whether it's a buyout package, a sign-on bonus, a relocation package), it depends on your leverage. How badly they want you. There is no one-size-fits-all here, but I do think the new employer will be open to paying something. I was paid a totally arbitrary sign-on bonus as an AN2 because I had a bit of leverage. 

Now I would add that if you can somehow justify what you're asking for, that will make the team more amenable to paying. For example if you have a credible bonus coming up that you can point.

On leverage, that's something that only you know, but keep in mind that the lateralling market is still weak. But also keep in mind that if this move is something you truly want to do, forget about the money. Even at your level, unless there's some massive amount I'm unaware of, this will be a rounding error 10 years from now.