If you're doing Hapkido, you don't need Aikido. From what I can glimpse of Hapkido, it is just not as graceful as Aikido. Depending on the style of course. Hapkido is basically Aikido minus [Chris' correction: plus lots of] the kicks. I think you will just get confused.
Right now, my focus is on Karate as Hapkido -- with all its kicks & strikes, locks, take-downs, and ground fighting -- programs are "spread thin" with its comprehensive scope.
I would like to add Aikido now to my workouts as my wife would like to try it and I've always been curious since I briefly dabbled in Davis.