If there is no restriction in his HOA rules then he can tell the HOA to go suck eggs.
Are this guys burglar bars HOA legal? Maybe the neighbors bars are HOA approved. They allow that type of burglar bars in my HOA but I doubt that they would approve the POS I see in that picture.
Simple. Read the HOA rules. If it's there you can't do it, and visa versa. If the HOA has quit enforcing the rules then it's open season.
BTW I'm glad this guy isn't near me. He seems to keep old doors stored on the porch, doesn't trim his bushes or cut the yard, and he lets his dog run loose... ;)