Yes, ECC can be unreg. memory. It can also be reg.

ECC but not reg. example:

KVR533D2E4/2G - Part Detail


Description: 2GB 533MHz DDR2 ECC CL4 DIMM


Detailed Specifications: Standard 256M X 72 ECC 533MHz 240-pin Unbuffered DIMM (SDRAM-DDR2, 1.8V, CL4)

Manufacturer #: N/A

Form Factor: Memory Module

Pieces/Unit: 1

Warranty: Lifetime†




Reg. and ECC:

Kingston 2GB
reg./ECC RoHS
KVR667D2D4P5/2G
Elpida
E5104AG-6E-E