I think "pro year" is the same as determining the elc slide.
Caps drafted Jacob Vrana in 2014. He played his D+1 2014-15 in Sweden, then made his north American debut in 2015 with Hershey. He wasn't protected or listed on the NHLs list of available players, so I think he was exempt from the 2017 expansion draft.
Reporting seems to confirm that he was exempt. It's sensible, too.
I'm forever mad they didn't publicize the actual legal rules, but only journo-reported abridged versions. NHL.com at that time knew to tell that:
"All first- and second-year professionals, as well as all unsigned draft choices, will be exempt from selection (and will not be counted toward their club's applicable protection limits)."
That doesn't much help with determining if the special cases are exempt. There's some crazy crap with late birthday players who were drafted from CHL and are playing in AHL, who because of the special CHL rules get their AHL year counted as pro year even if they're sliding their ELC. Our Gauthier will be one of these guys and probably will not be exempt.