Ok, Ed Bernard responded: He said that SSi was probably not involved with the ASIC if their logo is not on the die (plus he doesn't remember SSi doing it, and he was at SSi from at least 1975 through 1984), and the layer markings are probably from the chip fabrication house, rather than SSi (who I guess did mask layout only). Also, most SSi chips have Mxxx (where xxx is some number) on the die.
So it was laid out by someone else, but actually fabricated probably at the same silicon foundry as SSi used.
"When life gives you zombies... *CHA-CHIK!* ...you make zombie-ade!"