Nick,
Flexible metal conduit not listed for grounding can be used as a ground provided it is less than 6 feet and the fittings are listed for grounding and the circuits are protected at 20 amps or less and it is not installed for flexibility.
Flexible metal conduit listed for grounding can be any length provided the fittings are also listed for grounding.
By the way, has anyone seen how much the UL description of flex fittings listed for grounding and flex fittings not listed for grounding has changed from the 1999 book to the 2000 book? It is quite significant. There appears to be no special determination for steel vs. aluminum using set screw type connectors in the 2000 book like there was in the 1999 book.
