No. Nein, nicht, nyet, non!
To my own way of thinking, learninh how to be uke is fifty per cent of learning Aikido. Ukemi is far more, I think, than being a practice-dummy for nage, it's about learning how to move; how to control your body while falling. I believe it's also important to know how a technique - nikkyo for instance - feels when it it applied both correctly and incorrectly.
For that reason, too - (I just thought of this as I was writing that last line,) I think being good at ukemi is valuable for an aikido instructor - by not only being able to see what a student is doing right/wrong, by taking uke's place, you can feel it as well, thus better helping the student.