How you handle the question "Have you been convicted of a DUI?" is up to you, but were it me - knowing the slate has been wiped clean - I would answer "no".
I would be very suspicious if the question was framed "Have you EVER been convicted........." Only a real
pr!ck would ask it like that. The legal people here can answer whether or not anyone is entitled to ask it that way, and whether you are under any obligation to reply truthfully.
After all, prospective employers are no longer permitted to ask about your religious or sexual orientation so why should they be permitted to ask about civil or traffic offences that have been discharged by time?
'Spent' means 'all gone, done with, exhausted, finito'......So your spent conviction does not exist. You have every right to have conveniently 'forgotten' it.
Take a cue from Bill Clinton, who famously said: "Ah never had a sexual relationship with that woman" and got away with it, because technically, he hadn't. A blow-job is scarcely a relationship. It was the answer his followers wanted to hear.