It does seem like a second cousin to HAM. 
It's just a multi-palletted image. Probably closer to the DynamicHAM like that NewTek viewer used than a true HAM mode.
I'm not really sure what mangling the GIF format to do this really accomplishes, though. There's already a plethora of formats for high-color modes. And, of course, the only programs that can use this format must support animated GIFs. And, not much besides web browsers really do that, anymore. (And since browsers also support JPEG, TIFF, PNG, etc...)
I'm just not seeing a purpose here, other than, perhaps to win a bet about how many colors can be displayed in a GIF... ;-)
