Restoring logs from an obsolete-data folder
From what I remember, it can be done, yes.
You will have to rename the folder containing the logs though.
In obsolete data you'll have folders for each device type. In there you will have folders for each IP address observed, with some stupid number attached. Remove that number, copy/move the files back into the data folder, use lsmaint to re-index that device type completely.
Usually data gets moved to "obsolete-data" if you delete a device from the "manage monitored devices" screen. So if you didn't collect anymore data of that given device you would need to re-create it manually first, otherwise you will have no access to the data.