In what way would they not be?
I suppose at some point we'd need to have a discussion on what we mean by words like "attack" and "balance."
To expand on what Hugh said, I think of "attack" as morally neutral. An attack may or may not be aiki. It may or may not be balanced. My body's immune system attacks pathogens. When in balance, it kills and destroys in a proper proportion. When not in balance, its response is too little and I become ill. When exaggerated, I have an allergic reaction.
Predators attack prey. Success in survival is often a matter of being able to attack while closely adhering to a zone of balance. On the mat, we spend around half our time learning how to be the attacker, and none of this should be time spent outside of aiki. I might go so far as to say that without uke, there is no aikido.
Uke may sometimes simulate the bad guy, in order to help tori learn. But some encounters (on or off the mat) require us to be primarily uke, and in this mode I believe we still should try our utmost to exemplify aiki and the qualities of balance.
Just a thought.