Using 1 taxonomy for multiple post types?

You can use an array of post types in register_taxonomy()

$object_type (array/string) (required) Name of the object type for the
taxonomy object. Object-types can be built-in Post Type or any Custom
Post Type that may be registered.

http://codex.wordpress.org/Function_Reference/register_taxonomy

Example:

register_taxonomy( 'artist', array( 'profile', 'cd' ), $args );