Honestly, Givenchy Gentleman is such a CIVET BOMB (at least in its current formulation), that it's hard to say what qualities in it should be attributed to vetiver versus patchouli.
It's pretty common to find vetiver essential oil in natural foods stores and the like; so you could get a clearer "read" on the note by sampling the oil unblended. Keep in mind, however, that there are different types of vetiver (e.g. Vetiver Bourbon, Haitian Vetiver), as well as related aromachemicals like vetiverol and vetiveryl acetate. The search function can lead you to various threads discussing the differences among all these things.