Hour a day is kind of long unless you were really hardcore. I usually do 20 minutes a day on the pad, but I do a specific workout regimen and it ends up lasting roughly that long.
What does improve is your speed, dexterity, power, dynamics, and control on your hands. When playing grooves and fills on the drumset, I can play things I was playing before with more fluidity, more speed, and I don't get tired as easily. My drags now actually sound like drags instead of buzzes.
Now the downside is you aren't working your feet, so my bass drum is lagging behind my hands farther than it was before
but oh well, I'm still better overall.