Raki is, as I'm sure you know, heavily anise flavored. If you've got an ounce or two of it in your airlock, the whole thing could easily get sucked back into your fermenter, and I wouldn't be surprised if that affected your beer's flavor.
To my mind it makes more sense to use an unflavored spirit like vodka. You can buy a relatively cheap bottle of it and use that, that way it won't impact your flavor profile if it gets sucked back in.
Just my .02