Yes it is and while I can't test if it fixes the problem with VLK keys, it is at least clear that integrating XP SP3 on a Vista / Win 7 host will not fail in all cases as the guide seems to suggest.
EDIT: I borrowed my work's VLK copy today and did a test on it. The method appears to work, however because the copy is not clean (been nLited to preset serial, company name and regional options) this test is not definitive.