This is a topic that potters go around and around with. Moss makes some really good points, and I think that the answer is that it depends.
Oxides leaching out of the glaze would be my main concern. I've seen teabowls for sale that horrify me to think someone would actually be using them. Shiny copper or rainbow type glazes, BAD! In fact I would probably go as far to say that any colored raku glaze is not good (with the possible exception of iron being used as the colorant).
Now white glazes, clear crackles and such, I would worry about much less. However I would still want to know what was in the glaze. Glazes composed mainly of frit I would consider pretty safe. Tin used in small amounts to make the glaze an opaque white would be fine in my book (tin is used to line whisky flasks because of its resistance to acidity) The main thing would be for the glaze to be a fairly stable glass.
Another thing that might concern me would be the materials used for the post-firing reduction. Often folks use newspaper which has all kinds of nasty stuff in the inks used. These chemicals when burned have the potential to be absorbed into the clay, and later leach out. If natural materials like leaves, pine needles, or sawdust (from untreated wood) are used in the post-firing reduction I would consider that fine.
As far as the clay being absorbent with the potential to grow bacteria, well I guess that depends as well. What are you going to put in it? Raw sushi, would probably be very bad. Tea, not so much. If that were the case any teaware made of Yixing clay should immediately be thrown away!! Actually all clay (with the possible exception of a VERY vitrified porcelain) is still absorbent after it's been fired to 'maturity'. It's just a matter of degree. So, if you have any pottery that has a glaze that's crackled or crazed, the potential to harbor bacteria is present.
Man, I could go on forever, so this is my 2 cents for now. Buy your raku wares from someone who's knowledgeable about the safety of the materials used in their process and enjoy it!!