You can bet your sweet Ash it is no harder than any other woods, although it is an open pore wood and will require wood filler to accomplish a smooth surface finish.
Ash is commonly used as an Oak substitute in many a piece of furniture... in fact most of the "less expensive" OAK furniture is Ash, look for the "Flecks" of White Oak and it is not there, then it is Ash under the smock of an "Oak" piece. Most buyer can't tell the difference... We more brilliant WWers can of course recognize from across the room (yeah, right) I had some diningroom chairs (now my daughter has them) that had both Oak and Ash parts, without my "well trained" eye you couldn't tell the difference even down to the speckled on "worm holes" that some seem to think are so Cool... Stain and finish techniques can make any wood look great.