If the frame is Aluminum, it was most likley originally Anodized, although the photo looks like it was painted with some type of enamal. I don't know about Cerrakote as I have no experience with it. I wouldn't waste my time with duracoat.
Yes, Aluminum can be refinished. We regularly refinish Aluminum parts with our TG-1 finish with no problems. However, it must be abrasive blasted as part of the refinish job to remove the old finish, scale, flaking finish, etc. Abrasive blasting Aluminum has to be done by somebody that has experience with it. If they use silica sand, it's very easy to ruin the part. (Frame, etc) Silica sand will "eat" Aluminum. Even freindly abrasives can damage it if it's shot at to high of a pressure or aimed at one spot for to long. The idea is to remove all paints and matte the surface, not cause scallops.
It's a good idea to use some type of chemical Anodizing procedure on it before it's coated. We use Alodine. Depending on who you talk to, it's not quite as hard as "normal" Anodizing or it's harder. Keep yer powder dry, Mac.
Tuff-Gun Finishes. The Name Says It All.
Mac's Shootin' Irons
http://www.shootiniron.com