The following links are to a set of lectures by one Shihan in Korindo Aikido. They describe the basic pedagogical approach of Korindo Aikido.
In fact, at least in Israel (possibly due to cultural aspects), most beginners tend to be more resistive then they should and keep trying to counter and resist techniques, long before they or their partner gets a basic grasp of the technique.
Advanced students normally change their behavior according to the ques they get from Sensei on the purpose of a specific exercise. Thus we may either make a beginner technique work before he knows how to (Yundasha are required to learn this skill as a symbol of understanding techniques) or make life extremely difficult for an advanced student (either timing wise, or requiring high level accuracy or else one will follow the power out of the technique).
We train against strong grasps or strong and fast attacks from time to time, but, these are specific exercises done when both Uke and Tori know the results.
In Korindo Aikido we also practice "free play", with both sides free to attack, apply techniques and counter (Keashi waza) at will.
The following lecture explains the different stages of this practice:
I should mention that in fact, we tend to proceed to the advanced steps to soon, and Sensei has to keep hammer into our heads the purpose is to learn and not to compete \ prove ability.
However I would never call the above process "resistance training". Since we constantly train ourselves to avoid any resistance, our basic philosophy is that our opponent is always stronger, thus, if Uke resists one technique, Tori should simply perform another (and preferably utilize Uke resistance for the Kuzushi and next technique). Obviously, when doing Kata, this solution is not an option, and resistance can then be very problematic for a students progress (my slution is to return to the Kata, oftenafter showing Uke I have a different answer to his resistence