I've found that most commercial/industrial and even military equipment manufacturers often utilize bare spots (near a fastener) in coatings for earth grounding.
The bare spots may have been masked during the coating process, or more commonly, a spot that's been hit with a ginder or sander before or during the assembly stage of manufacturing. Sometimes the bare spot(s) may just be the around the corner attachment hole in a panel or cover. Some variations include a (forget the name) lock washer that ensures penetration of the oxidation that may be present on an aluminum panel.
If a panel is secured in place with nuts, kepsnuts (with integral lockwashers) will make a secure electrical connection (provided that they're tightened properly after any servicing is performed).
Another common method is adding a headless screw post to a panel for a ground lead to be attached to. These are the pressed-in studs which are nearly/almost invisible on the exterior surface. The grounding posts/studs are generally a chassis feature, but sometimes used on a cover panel as a secondary earth grounding tie-point.
The bare spots on mating surfaces can be accomplished with a Dynabrade or Dremel-type tool with a sanding drum.. a fairly effortless step that can be accomplished in seconds.
Vibratory tumblers can probably provide almost any desired finish by using a specific abrasive compound.
Don't know about the alodine process, although I may have seen it and not realized what it was.