It seems to me that this pinout chart matches what most people think is correct.
That said, the linked cable should work. I'm not sure about the TI-99/4 (non-A) version although the linked page lists it as well.
As for Sega Genesis cables, it seems that you would get audio by attaching the RCA plug meant for Sega video into your audio input, but unlike what the TI Guy posted above, I can't figure out how you would get TI video by using a such cable. Not that it matters much since you should avoid using a such cable in the first place. Note though that on the Atari and C64 you would get a B&W image from the luminance signal on pin 1 using a Sega cable in reversed mode, but on TI as well as VIC-20 etc you would be feeding a 5V-12V signal into the TV.
Sorry, i was thinking and the systems got reversed in my head.