Quote from the book.

Sometimes people want to do spells involving the saints, but confess to me that they aren’t Christian and want to know if it’s ok. Its funny how, this only happens with Christian figures. Nobody seems to care that they aren’t a Buddhist or Hindu to work with Kurukulla or not an ancient Greek to work with Hekate, but because we live in a Christian culture, working magick with the saints or angels can seem more taboo. My advice is this: just do the spell with devotion to deity as you understand it, but do it according to the rules of the tradition it comes from. In other words, do not call upon St Martha in the name of Artemis or Odin. 

She won’t like it. Just as its impolite to visit a foreign country and demand that everyone follow your customs (though I have seen that often enough), its impolite to call force Saints and Dakinis and Spirits and Loa and whatever into formats that they aren’t comfortable with. After you make contact, you can work out some different conditions with the spirit, but don’t approach them that way from the start.