That is certainly outdated advice. Most doctors, these days, would say it is fine to father a child on imatinib. And the conclusion for the other TKIs is rapidly going that same direction.
I would urge you to watch this video of these slides. It's by Jane Apperley, who is one of the foremost authorities on this particular topic.
I'm on dastinib, and spoke to Jane about fathering a child whilst taking it. Her advice was "just go for it", even though I do have sperm in the freezer. That approach bore fruit ... well, two fruits, but that can't be blamed on the TKI!
David.