Oh yes, they do actually, haven't checked in a while, have they started to accept fiat deposits this year? Then CRS questionnary was only logical of course. I only tried to withdraw usd from bitfinex once and it took 45 days.Bitfinex support fiat trading as well as usdt.
The simpliest way for report for exchanges is a make balance reports snapshot for date 31.12 at market rate for all crypto assets.
Maybe they are simplify report and send only fiat balance that was on 31.12 on the account, but its to simple way for avoid any summ in reporting, so I doubt exchanges will do this way.