You should be able to. All that moving the tape over to scratch media does is remove any current overwrite protection or append periods which were applied to the media through the relavant media set, therefore making it available for use. But it doesn't do anything to the tape itself or it's contents. In fact I don't think you even need the tape to be inserted in the drive / library in order to move the media set, so it can't make any changes to the tape.
I think your problem is something else, eg the catalog job isn't correctly reading the data from the tape to display it in your restore selections, or something went wrong with the original backup so the data wasn't even backed up correctly. I don't think it has anything to do with moving the media over to Scratch Media.
