It could depending on what your going to use them for. Olive oil burns rather easily and produces more smoke then some others. Vodka is more for extracts, not oils. Olive oil will often leave you with a stronger scent, so it is not as good for aromatherapy purposes.
I have used olive oil to make essential oils for hair and skin treatments, because it works wonders on your scalp, hair and skin. If you are using it to mix down premade oils, I would use a 25/75 ratio, with the olive oil being 75% of the mix. If you are making home made, soaking a few tablespoons of the ground herb per cup of oil and letting it sit (make sure to shake it up a couple times a day) will usually suffice.