Nope, not scale but the prominent lenticels typically found on the bark of hydrangea. All woody plants have lenticels...some are more noticeable than others.

a scale .. can be.. lifted/peeled off ... like those old candies on a receipt ...

those bumps.. are far as i can see.. and some pix arent great.. are part of the bark .. and the only way to lift them off.. would be to break the bark ..

ken

Here is a link that might be useful: who knew they had a name.. lol ...