What options are available for using a GeoTIFF as a background layer?

You can load GeoTIFFs in Merkaartor.

This doesn't seem to be explained very well in the documentation (I think its a fairly new feature), but to do this:

• Click on the Layers menu, then "Add new image layer".
• Then right click on the "Map - None" layer in the layers dock, select GeoTIFF, then "Load image", and pick your .tiff file.
• Then your image should be loaded. Note the map view will not change to where the GeoTIFF is, you will have to manually scroll/zoom to the correct place.

I never did this before but I think http://warper.geothings.net/ may help you to provide a WMS layer that can be used as Background-Layer in JOSM and Potlatch.

To display your GeoTIFF as a background layer, you need a way to convert it to a coordinate reference system (CRS) suitable for the editor you are using. For JOSM, the ImportImage Plugin will take care of transforming your images to the CRS used by JOSM.

If the only thing you wish to trace is a USGS topo, JOSM already had that as an option under the imagery menu pull down. Not sure about other editors. Near as I can tell from the areas I've looked at the scanned topo images are from the most recent USGS versions.