Is it true, can I really back the front drive axle out of the hub on my '97 tahoe without even removing the wheel or parting the balljoint? I don't want to start this project in the rain if i need to disassemble the entire front end

No, it isn't true. You have to create enough working room to get the old one out and the new one in. Upper ball joint is the easiest way to go.

Is it true, can I really back the front drive axle out of the hub on my '97 tahoe without even removing the wheel or parting the balljoint? I don't want to start this project in the rain if i need to disassemble the entire front end

Most of the time you can.
Some the swaybar link has to come out to do it.