There is no hard and fast rule. Some dojos have weapons classes, but I suspect the norm is as with us. I should point out that we come from the Yoshinkan, but not all of our dojo are IYAF.
Our classes are simply "Aikido"! So the class can be any aspect. When I teach a class I plan it around how I see the need. I always feel that weapons is something that a student should follow on their own with the guidance of their teacher. My reason for this is that there is a lot of solo practice required. Once that a student is adept with the sword or Jo, then the value of weapons can be found.
The sword teaches center, hip power, focus, etc... and with a partner adds timing and maai (fighting distance). Jo is different. The solo practice teaches focus, but in Jo Kata the postures move into different forms from our empty handed Aiki. Things like back-stance, etc., but these teach us a flexability in our movement. It is all extra to what we do, but it must all approache from the way we approach all our Aikido. If we "do" Bokken, then "do" Jo, etc., then we limit ourselves, but if it is all AIkido, then we build on everything else and grow.
Tanto teaches distance. In our school we do Jiyu Waza (parallel "randori") with a "real" Tanto. This absolutely teaches distance as it removes any margin for error.