I said yes for completely different reasons to the above. To me ukemi practise is very similar to being a nage because you 'blend' with the floor. I also think it is important to get the feeling of extension during (rolling) ukemi, which distributes the weight evenly around your rounded body, rather than landing on your shoulder. I think extension (& technique) and ukemi compliment each other and improvement in one helps the other 'cos it is the fundamental concepts which we use in everything.
As far as resistance is concerned I like neither the 'cooperation' camp nor the 'your job is to try to resist the technique' camp. All dojo practise is unrealistic, but to me the aim is to improve technique to the point where it becomes as useful in real situations as possible.
Therefore I advocate the concept of 'mild nage frustration technique'. i.e. As uke it is your responsibility to encourage nage to learn and develop effective aikido. By blocking him, countering or resisitng a throw repeatedly nobody learns anything. It can be thought of as stages, though it is obviously catered according to the ability of the nage with the specific technique, and whether this is the first throw with the partner of you've done several and are into the rythm of it:
1. you go through the motions with nage so they learn the mechaniscs of the technique.
2. you attack hard, with no feeling of 'regaining balance' (which is quite realistic in most cases, as people on the street rarely know you are going to do any aikido technique, let alone a specific technique).
3. you attack hard but try to retain your balance (but without any counter movements). This is often necessary when you are relying on ukes reaction to protect himself to perform a certain techniques.
4. you attack hard but gently push nage or regain your centre or regain control of your own arms (during applications) or use strength to remain unmoved to illustrate areas of weakness in the technique.
And only as part of the class instruction:
5. You break off or roll out of a technique (to show areas of limitation which may be intrinsic within the technique) - this is best accompanied by additional techniques for Nage to react to such a response by uke.
6. Counter techniques.
I call it 'mild nage frustration technique' because Nage should constantly be recognising limitations of his technique, but should not be discouraged to the point of actual frustration; otherwise they never get in to the real movement of the technique.