IMHO, all techniques lend themselves to training aiki if you focus on the subtleties of connecting, blending, and taking balance. All waza can become kokyu-nage (breath/timing).
I disagree, Lynn. If all techniques trained aiki, then there wouldn't be such a commentary going on by all of us who have gone to meet Dan, Mike, Rob, or Ark. You can't get aiki by focusing on the subtleties of connecting, blending, or taking balance. You can't get aiki by training techniques. Being soft and being relaxed isn't going to get you aiki.