I think kai said that goku was the only one of the z fighters (or anyone?) capable of learning kaioken. Possibly because of the hard strain on the body, or the advanced level of the technique was too much. Either way, you never see any of King Kai's tons of students use kaioken. It doesn't seem like something just anyone can learn, even people like tien and piccolo.
I think Tien and Chaotzu might have actually stayed on king kai's planet for at least a year or more. I remember something about the end of the freeza saga involving people getting wished back. I think Tien and chaotzu were wished back last, and they had to wait a year since earth's DB's needed to recharge (they made a LOT of wishes... get back freeza's victims, move the nameks... that's a few years)