Of course they "can". But they are two very different things: Aikido is a means for self-defense, and many of its techniques derive from use of a sword. Kendo, on the other hand, is a sport. There are almost no common principles, other than holding the sword.
Therefore, the Aikido-ka who knows a little about the sword must train as a Kendo-ka does, and that means, starting at the beginning. The skills one trains for in Aikido is hardly transferred to Kendo. The footwork, the strategy, the attacks and defenses - they are all very, very different.
Remember, there are no aggressive strategies in Aikido. Kendo, conversely, requires aggressive strategies in order to score.
EDIT: Ok, no, they cannot. Not without significant training at least. If Aikido-ka do learn sword use, it will be with a bokken (a wooden sword). Kendo-ka may use a bokken from time to time - but their primary weapon is the shinai - a bamboo stick. It is exclusively with this that they compete. The techniques, the weapons, the foot movements, the dress, the strategy, the etiquette... there is almost nothing in common.
One who holds a dan (or any) grade in any style has no guarantee they can assume that rank in another school - even of the same style. In your case, though, the styles are not only different, but they aren't even similar. Aikido-ka don't learn the "way of the sword", they only learn some sword techniques from which their techniques derive. Some schools follow O Sensei to the letter - and they don't teach weapon use AT ALL.
As to jujitsu, many techniques are similar. Further, some jujitsu schools compete, others do not. For those that do, the philosophies are very different and it's a sure bet you won't be allowed to assume your Aikido rank. For those that don't compete, it will be up to the instructor... just don't bet on it.
Possum gave a great answer. I just want to be clear. An Aikido Ka can't just sign up and be in a Kendo tournament. He must train in Kendo to be in a Kendo tournament.
Is that possible someone that know Aikido or Jujitsu,join in kendo matches? because they both learn the way of sword too.
