Yes, it seems OK. I’m copying my data (LibreBoard 0.8 from OVH/RunAbove 1-click-app) to Wekan 0.9 (OVH VPS SSD)
As stated in Docker’s doc containers should be ephemeral, i.e. should be stopped, killed and restarted at any moment, so the technique is to use volumes (as you already know for sure). I looked at the Mongo page on Docker Hub to see where to store data and followed their recommandations.
I don’t have particular experience on this, except I verified it actually works: I used a volume, added some data into Wekan, stopped the containers, restarted them, verified data are stille here, everything went OK (repeated 3 times, you never know )