Yes, noticed it on a thread myself, then tested on a fresh one. Also had someone else confirm it.
Find a deleted thread with a poll.
Vote on the poll.
You'll see your vote registered, even though the thread is deleted.
I expected the thread to show "Poll is closed", as it does for normal users when they enter a locked (not deleted) thread with a poll.
This isn't a big deal, since it only applies to Staff members, but since we do have a "Poll is closed" option in place (outlined briefly above), we may as well implement it.