The first hotel I looked up states that the restaurant is opened for hotel guests. Breakfast and Dinner.
https://laaxerhof.ch/en/
Are you looking at the info while doing reservations (where you decide whether you want breakfast included, but dinner is not always an option)?
I then looked up a restaurant in LAAX where I ordered takeaway a couple of weeks ago (Nooba) and and it states that they are open to hotel guests. I am not sure if they mean the Rocks Resort only or, the adjoining hotels too (like Laaxerhof above).
I walked pass a few hotels in Flims and Laax a few weeks ago and all hotel restaurants seem to be open but I could only get take away because I wasn't staying there.