According to the manual:
"A block-level incremental (BLI) backup recognizes that a file has changed based on a timestamp and checksum algorithm".
So i guess archive bit is not used in traditional BLI backup method in any version including v3.
About changelog minifilter driver it only says:
"Open Systems SnapVault scans the backup folder to identify the changed files".
IMHO this can be understood the similar way - that still timestamp is used.
Hope it helps.