Lisa, a drum sander will take the tar off but it will also gum up the sandpaper on the drum. I would not worry about getting everything up before sanding but I would want to get a lot of it off to cut down on the labor and expense of replacing the sandpaper.
When you do start sanding, you will want to watch pretty closely for nails in the floor that have popped up or are uncovered by the sanding. Those will tear the paper and the drum up also. Have a hammer and nail set handy to bang the nail heads down into the wood.