I’ve never used gravel versions, but roller ski training, in general, is great for skimo. If you can glide a roller ski, you can glide a skimo ski.
Separate from learning to glide a ski, the challenge is finding steep roads to train on and, if found, getting back down. I used to use three bikes and a vehicle as shuttles. (The thought of going down steep roads on brakeless roller skis is terrifying.)