The registration does not define whether or not an aircraft is an EASA aircraft. An EASA aircraft is any aircraft type that would have an EASA CofA if it were registered in an EASA state, so a PA28 / Cessna 172 is still an EASA aircraft even if it is in Aus & has a VH registration. The CAA rule allows hours in other aircraft, eg homebuilds, to count towards re-validation.
The second quote by Curtis, the interpretive material, points out that an FI is only an FI for EASA purposes if (s)he has an EASA FI certificate. So, no, an hour with an Australian instructor will not count (unless he has an EASA FI as well.)