OK, it is the chipset, not the DIMM, that does the actual ECC work; the DIMM just provides extra bits -- 72 instead of 64 -- to store the info. If ECC mode is enabled in the chipset, the chipset automatically calculates the 8 bits of parity info and stores them along with the 64 bits of data. When it reads in the 64 bits of data, it automatically compares the newly-calculated 8 bits of parity with that read in from the DIMM.
Thus, there is no functional difference between the 64 "data" bits and the 8 "ECC" bits in the DIMM. If ECC mode is supported for your chipset and is turned on, the 8 bits get tested just like the 64 others, by comparing the value read in from them with the "correct" value.
Memtest86+ monitors the ECC process for at least some chipsets. You might try contacting the good folks on the memtest86+ forum to verify if your chipset is supported.