That almost doesn't look like mealybug to me, especially considering you said it doesn't seem to move, but I know this particular Hoya is prone to them.
Did you try plucking one off and turning it over, to check for legs? How about poking it or squishing it (it will release something if it's a "bug")? I realize they don't really move a lot because they're a sucking kind of pest, but if there's no legs present (or body for that matter) when you flip it over, that's perplexing.
