It is common practice to prime and paint cad plated bolts. The cad plating actually is a good base for the primer. No additional prep really needed. Just make sure that they are clean of any grease or oil.

Go take a look at any production aircraft and you will see all of the AN bolts painted by the factory (Cessna-Piper-Mooney-Gulfstream...).

Best of luck,

Wes
N78PS