I think that any physical activity will help you out. I remember that when I would get done with Aikido I would be all sweaty.
Also, I read "The Invincible Warrior" by John Stevens and it talked about how much physical work that Ueshiba did to get stronger (cutting would and hauling it, etc.). I have also read stories about even when Ueshiba was older when he grabbed your wrist it would leave a bruise.
I think that there is a fine line in Aikido. The body should be strong, but the techniques should not rely on that strength. It's almost an oxymoron. The stronger the body the more relaxed and fluid it can be because there is less effort to move.