No, that is rare. Of the many, many people I know personally that do various different style of Iaido and Kenjutsu, most did not study any Kendo. Besides Kendo techniques do not use the slicing motion that the Katana requires to be most effective. A good example is the fake sword demonstrations that are seen often at Karate tournaments and martial arts demonstrations. I'm referring to the demo where some bozo with a katana slices a cucumber, watermelon, or some other object. They place the target object on a volunteer that is suspended on their back on two chairs. This is fake because the sword is a slicing weapon, NOT, I repeat, NOT a chopping weapon. Anyone can chop a cucumber of other soft target placed on someone with little risk to the volunteer as long as he does not use a slicing motion to cut. My own Katana is razor sharp and easily slices if used correctly. But to demonstrate that it is not a chopping weapon I will pull my sleeve back and bounce the cutting edge off of my forearm.

...

I read in other places that some people were required to learn kendo before entering iaido and I didn't find anything suggesting the contrary, also I wanted to know if it's best I do kendo and for how much time should I do Kendo before starting iaido. I also wanted to know which is the best battoujutsu or iaido and how time it takes to learn them.