Currently not. But compatible classes are worked on right now and will be available when ready.

Also interested in this! We have 3 players playing gloomhaven characters in our Assisted playthough right now. Very excited to make the switch once either the gloomhaven characters are added or my playgroup is all back on frosthaven characters again.

(For those wondering, we retired our FH characters without unlocking enough new ones, and rather than replay classes, we decided to try out som GH classes we never unlocked in our GH playthrough!)