I do not have first-hand experience with this, but it's my understanding that the AAU ratings only indicate the bittering potential of the hops. Like MarshmallowBlue said, for bittering purposes, you should be ok (ignoring things like AAU loss due to aging, which may affect one variety more than the other).
Since you're talking about the flavor/aroma, I guess you might be using these for later additions. In that case, 4oz vs 1oz are likely to be very different. For bittering, you get an effect proportional to efficiency times AAU times mass of hops. For flavor, you'll get a "flavor efficiency" times mass of hops times "flavor units."
For bittering, your efficiency accounts for the boil time, contact area, etc, and the AAU rating accounts for the potential in the hops themselves. For flavor, you'll get a similar effect. What I call "flavor efficiency" would cover the boil time (though unlike bittering, shorter times will give higher efficiency). The "flavor units" would measure the quantity of flavoring compounds that can be extracted from an ounce of a particular variety/batch of hops in the same way that AAU does.
Now, whether the flavor units can actually be defined or measured in a useful way, I don't know, but my point is that it's going to be very hard to do a calculation to determine whether a substitute will work for flavoring. Certainly these properties of hops are not as well documented, so you'll really have to go by trial an error and experience to figure it out. My advice would be to be careful to match the bitterness, and note the flavor/aroma results. You may wind up with more or less flavor, but as long as the bitterness is on target, you won't find yourself with an undrinkable puckerfest.
