All PS3 are HEN compatible.
12GiB models have internal eMMC. It probably uses VHDD in the same way as VFLASH on NOR models. So what normally is written to HDD, in those models is written to eMMC (until user put HDD to the slot, then it will be asked which storage You want to use; if You choose HDD, then all user data from eMMC will be copied or moved).