Image in "drop image" does not show up in FCP.

Normally you do not "load" a drop zone with media in Motion, but it is a viable option. The trick is, when you save the project as a template, you have to select the "Include Unused Media" option so Motion will save the drop zone media to the Media folder in the template so that it is available for FCPX.

You are encouraged not to do this as the drop zones are available and are usually "loaded" in FCPX unless you have a good reason to do otherwise (example, forcing an aspect ratio sized zone image or a specific "default" image or clip for the effect).

If the drop zone-looking background says Title Source, then that's not really a drop zone. That's a placeholder for the storyline media (technically, with a title, it's everything below the level of the Title object... but that's a bit of nitpicking).

If you want to add a logo, try adding your logo directly within the Motion project above the Title source sized as positioned as you want it. You might also publish the Position, Rotation and Opacity parameters for the logo so you can animate it in FCPX in custom ways without having to go back into Motion every time you want to make changes.