I voted yes, because I think that while doing the specific technique you were asked to do, you sometimes get problems that would never occur in jiyuwaza simply because the uke knows which technique to expect and can do almost anything to prevent you from doing it, like punching to the left/right instead of punching straight because he/she knows that that's where you're going to move.
I think that on such occasions, uke should be told that that's really not the best idea to continue doing so.
It's really stupid if such a thing happens on an examination, though, (esp. for kyu), as if the uke doesn't want you to perform the given technique you simply can't (if your techniques aren't flawless, of course), you can change it or hurt the uke but that's it.
And anyway, I think aikido is about adjusting the technique according to what uke is doing, so if you're supposed to be doing a given technique the uke's attack should be enable you to do so, at least to some extent